A project lathe

by Marty Nissen

Lathe Bed Preparation

A 14" bed extension kit was ordered from Chris Wood at Little Machine Shop, part # 1928. Nearly all critical machined surfaces had some rather thick paint slopped about on them and this would have to go. The worst of it was in the area inside the webbing where the tail stock would register. Stripping required.

First a critical dimensional check. The beds are ground so a point of reference for the grinder is needed and this would be the foot area. This makes it fairly straight forward to qualify the casting by placing it on a surface plate first checking for rock, indicating a twist and using a height gauge checking for bow or warp and flat/level relative to the surface plate and the "V" way relative to the flat way. The "V" requires multiple checks as angles are involved and the top of the "V" in truncated. This was done with the top half of a bed lock as shown in the photo below.

Marty Nissen's 7x14 mini-lathe project - The lathe bed

Once the "V" is qualified then direct micrometer measurement from the top of the "V" to the lower bearing area for the saddle gib area is assured. If the "V" is not qualified then the bed lock block and micrometer is required for thickness checks. This bed checked out dead flat and all relative positions in alignment except that the lower bearing block area for the saddle gibs, which are milled and not ground, displayed slight thickness variations which will be corrected latter when the saddle is fit to the bed.

After the checks were done the entire bed was stripped inside and out. Machined exterior surfaces were masked withDuct Tape to prevent nicks and dings while the rough handling was going on, there is no gentile way to do this. A spraytype stripper for epoxies was used as gel types were quite ineffective. Small brass bristle brushes were required in therough areas of the internal webbing and motor mount areas and repeated coats required even then. A good washing in a bucket of mineral spirits followed as well as allot of fine filing of the burrs and sharp edges.

No serious voids were uncovered but a good deal of casting sand was eliminated during this step. The part, sand cast,uses about a dozen cores, none of which line up well. Ergo there is a good deal of very soft filler used in the worst areas.As you can see from the photo just to the left of the height gauge most surfaces not ground or left natural, are fly milledand not gently. None of the red you see in the photo was present after stripping. This is a thin coat of auto body glazeafter sanding with a block sander. The interior of the webbing and motor mount areas are already painted with Glyptal electric motor insulating paint. It's tough and quite resistant to oils.

Painting the interior is a very tedious task and very time consuming. Masking the machined areas is nearly impossible so a steady hand, small art brushes, lots of angles of attack are the weapons to prevent re-coating the areas you just spent so much time stripping.

The bed as delivered weighed in at 25 lbs. After stripping and knocking sand out of it and removing soft fillers, 24 lbs. The 14" beds have several more internal webs and the right foot is fully cast unlike my short bed machine. The motor mount area is wider to accommodate the larger motors normally fit to these machines as well. Both feet of the casting are also longer.

With the bed initial preparation completed and measurements qualified the next task is to fit the saddle assembly. Don't under estimate the importance of all the detail work. Everything references from the bed of the machine, if it isn't right, nothing else will be either. T'is the very foundation of your project.

Fitting the Saddle

Marty Nissen's 7x14 mini-lathe project - Fitting the mini-lathe saddle

Using the height gauge a near side reference is marked to locate it in the same position each time. Height is set from the base of the compound dove register as this is referenced not only to the bed but will be the reference for the compound later when fitted. Note I used the gauge foot extension to do this to get as much distance between points as possible. Once zero is set the height gauge is rotated to the back . A dial indicator on magnetic base set and zeroed. Now pressure is placed upon the near side of the saddle (operator side) using the "V" as the fulcrum which will lift the back side until it contacts the height gauge and down hill distance can now be read directly from the dial indicator. When this was first done the back of the saddle was .018" lower than the front!

The height gauge can be moved to the opposite side to detect difference in compound dove base height. In this case a few thou in difference.

Next the measurement equipment is removed form the bed and finger pressure applied to opposite corners, such as front left and right rear to detect any tendency to rock and there was. Use of the dial indicator or a feeler gauge can quantify the amount. Roughly .005" in this case.

Next one must identify the high spots and points of contact. Layout die applied to the saddle "V" and back flat and then setting it on the bed and sliding it back a forth a few inches will mark those places.

As side to side was pretty close I assumed the "V" to be pretty close in that plane if but considerably high and the major problem area to be the back flat. As it turned out the "V" area was making contact on both sides but with little area in contact. The back flat however removed next to nothing of the bluing. Just a light pencil lead width concentrated on the high corner. As it was so far out I used a medium sized second cut file to knock it down. Easy, a few licks at a time and checking. This whole process is slow and painful. Once the rocking motion was close to nil a piece of wet/dry paper, 80 grit was placed grit side up on the bed under the flat. A piece of paper over the "V" to protect it and the saddle worked over this until all trace of rock was removed. (Reverse of the top right picture) Of course this makes the down hill condition even worse but full line contact made across the flat which also corrected the side to side difference for compound dove register.

I had Kresser Machine run a quarter inch end mill down the roof of the "V". The reason this is needed is that the top flat of the "V" is about .200" wide (6 mm) and the relief in the roof of the "V" is but .157" wide (4 mm). As you attempt to remove material from this area to lower the saddle a ridge is formed that prevents progress. To be honest I didn't do this procedure straight away but it came as a consequence after working this thing silly for a week with little progress. A bit more thought on this and the roof height would remain as is as it is the width I was after.

Okay so now we have the rock out, side to side squared up and some room in the "V" to work with, now the hard part. Wet/Dry paper is cut to width to just cover the "V" and Duct Taped in place and WD-40 applied before the saddle is set down on it. On the flat several folds of paper are placed between the saddle and the flat.

The paper not only protects the un-lubricated flat but adjust the height. If you don't shim it like this or make some other provision for height then as you sand the saddle "V" it will eventually take a new angle and not one you want. This takes awhile to get a feel for, allot of tape and allot of sand paper and allot of paper towels allot of solvent and a lot of patience. Work slow and measure often as was done in the beginning. How many sheets of paper? Well a sheet is about .003: thick and were down about .021" at present plus the thickness of the sand paper so roughly eight ply will be close and close at this point is good enough. You want to be slightly high on the side your working and work it until your lightly low, then remove a single shim and do it again.

Measure, measure, measure...this took about an hour a night for nearly two weeks. Measurements will help you get a feel for pressure, how many strokes to remove how much metal, what grade paper to use and so on. Nothing I can give implicit instructions too and each case will be different.

Marty Nissen's 7x14 mini-lathe project - Fitting the mini-lathe saddle

When you get down to less than say .005" on the down hill trade the shim stock for a sheet of wet/dry on the back and do the same on the front, trade sand paper for a paper shim. You've reduced the angle enough to get much better contact and now you need it flat. Work both sides using a courser grade on the "V" than the flat. You'll get a feel for how much, where and when to quit long before your in trouble. (Remember, grit side up :)

If you got all this, by now your within .0005" or so of down hill, no rocking motion, both sides within .0005" in height and using something in the neighborhood of 320 grit paper.

At this point it just wiggles the dial indicator so I gave both sides a few strokes with a sheet of 1500 grit, then cleaned and again with 2000 grit, both with a liberal spray of mineral spirits and cleaned a final time.

When finished I had full contact on all contact surfaces that would remove blue (actually a Sharpie at this point) on a single passing. When wet with WD-40 I placed the saddle at one end of the bed and gave it a tap. Don't do that, it slid like a puck on an air hockey table crashing off the opposite end onto the bench putting a ding in the saddle that fortunately for me was in a place of no harm. Now WD-40 isn't the normal oil to use on the bed and heavier oil does induce more friction and the slide is less free. Acts like a joy block actually. Slides freely but near impossible to pull straight off the bed. When I was close the dial indicator was replaced with a test indicator with four decimal resolution and I ended with a wiggle in the indicator for down hill. Under .0002 side to side and zero rocking motion. Rechecking with the height gauge on all surfaces and re-qualifying the "V" with the bed lock block produced no measurable differences.

The finer and flatter the finish, the more precise the alignment (with the appropriate lubrication) the tighter things like gibs can be set limiting motion and precluding chatter and the lighter the oil that can be used. Joy block type finishes actually help dampen vibration using the elastic nature of the fluid as a shock absorber. Such surfaces wear at a much lower rate due to low contact unit loading.

Now, this is what I've done and I won't preach that as gospel to anyone. IF you disagree finish to what you like and use what lubricants you like, just get it flat and square and well aligned. Your now caught up to the current state of the build.

3/22/2007
Rereading some of this I see I miss explanation of a very important step. Cleaning up the dimensional differences of the bed underside gib contact area. This was done by making measurements along the way both front and back in half inch increments writing the dimensions with felt marker on the bed. Using a 4" second cut flat file the high areas were taken down as far as I dared. The the file wrapped in wet/dry 320 and worked until I was within .0002", This took several days and allot of measurements. I was concerned about getting out of square but gentle pressure working short areas at a time seemed to work just fine, even with out a guide fixture. Now the ends of the bed on both ends taper to a smaller dimension that the area I worked but I reasoned that only the area covered by saddle travel need be worked over. Later during gib fitting I used yet another method to finish the underside to an immeasurable tolerance.

Fitting the Saddle Gibs

Marty Nissen's 7x14 mini-lathe project - Saddle gibs
rear gib

Marty Nissen's 7x14 mini-lathe project - Saddle gibs
front gib

I made the gibs close to my own drawings from A-2 house scraps except thicker .350", and omitting the center hole. That made it 3.15" between centers on the two remaining holes.

The manufacture of the gibs was very straight forward and went off without a hitch. Installing them was another matter. I bought some brass shim stock and a set of feeler gauges to sacrifice for same. I also acquired a few sheets of 320 grit orbital sander media with the sticky back like they use in body shops. This turned out the be a very good idea. Nothing is square on these machines and the gib registers were no different. Use of a single shim proved unworkable as the registers are .001" out of parallel with the bed end for end. This translates into one end contacting the bed and the other quite loose making the gib dig into the bed. I reasoned at this point the two shims moved outboard of the fasteners of different thicknesses might work quite nicely and it did. Once it got it pretty close I disassembled the unit again as I had yet a few tight spots here and there. Using the gib as a template I cut sections of the sand paper the full length and width of the gib and applied it sticky side to gib, grit to bed and reinstalled the shims. Running the saddle up and down the bed then hits only the high spots. If you remember I had it down to about .0002" to begin with but when you get things this close even that is too much. Both front and back are now with in .00005 to .0001"" flat and parallel to that same dimension from the top of the bed and that is as fine as I can measure.

High spots gone the saddle fit a tad loose again so the shim packs were thinned a bit more. Thing is that sometimes you need a shim in some size other than standard .0005" increments. That's where the brass stock, a lapping plate and some 2000 grit wet/dry earns its keep. Now anyone who has ever done a bit of this close work would tell you that even bolt tension will move things a bit and the idea is to get a shim that allows enough torque to be applied to it to prevent loosening during use and that takes a bit of trial and error, I remade shims more than once. I might mention that clean is highly important as well as at this level of fit even dust on a shim makes or brakes it. I use brake cleaner and lint free rags. Oil has thickness so it need be cleaned and oiled each assembly cycle with the oil you are committed to. I'm committed to ISO 68 way oil and the supplier is unimportant but use the same one.

I remade a rear gib and made it 6" long X .4555" thick and 1.030" wide. Only the length contributes to contact area however. Extra thickness for the extra length for stiffness and width because I was too rushed to mill it off. This time I also used all three holes and located two stand off set screws as per original except that they are centered perfectly and in line with the three hold downs. These were made 1/4-20. Upon installation I fit the center bolt, placed the shims as before on the outside corners for level and gap. Then fit the two outside caps and played the bolt tension until satisfied. NOW I ran the set screws in to make firm contact and tightened the lock nuts. Finally, as both sides of each retaining screw are now supported those can be tightened to a sufficient level to remain in place.

The difference is night and day. Stick is gone and slip is even better. You would have to feel it to know what I mean and I don't think a video would make the point. A test indicator on the back shows ZERO displacement of saddle to bed and something under .0005" on the front. Placing and inclinometer on the bed and elevating until the saddle moved gave a slip angle of 7 degrees for a frictional coefficient of .121 "stick" and maintained motion once underway to a 5 degrees slip angle for a friction coefficient of .089. This is about a 4/5 reduction from factory in dynamic friction.

Note: the shims widely spaced and not full length but they are full width to prevent rocking. The rough measurement for shim thickness is above each but a bit of fine tuning on a sheet of 2000 grit with thinning in increments of .0001" per fitting was required to get it right. Of course that means I had to make each one twice and you over shoot the dimension one step the first pass. The different thickness is required as the saddle casting is not parallel to the bed at their mounting face.

The six inch length was a vast improvement over the standard 3.9" stock and 4" X .352" thick version. The extra length will preclude the use of the motor guard but I don't plan on the stock location for the motor anyway.

Note that the area for the cross slide screw is milled out in anticipation of a thrust bearing in the collar later. The extra length is .250" and the slot width is .804" provided by a reground 7/8 end mill which was the closest thing to a 20 mm in the shop. While I touched of the mill to go no deeper than .002" than the existing floor of the channel the extra length broke through the "V" roof which was raised .025" and widened .250" to drop the saddle earlier to get the cross slide dove rails level to bed. I could have gone back further as other have but I want to keep the tool inside the rails. I will epoxy a disc in this location to prevent chips from entering the "V" channel as this become exposed when the slide is extended with the bearing modifications.

Note the even oil film on the back way? Full and flat contact! Fully adjusted this saddle will slide right off the end of the bed and go right back on without a hitch with even light drag all the way to the head stock area even though it's fit to near zero gap.

Several notes in this view. Note how close I got the gib width to the bed casting? It's all about stiffness and surface area, especially on the rear gib. I will shorten the stand offs latter now that I have the shim pack sorted and add some thin washers under the jamb nuts as I did the button heads.

Before you ask, yes the apron will bolt up flush BUT the rack pinion will not rotate. Instead of creating a stress riser by carving on it as the taper gib arrangement does, I will turn the excess width from the gear. It's about twice as wide as the rack and the shaft proper does clear this fit buy .002"

Button heads again for a cleaner look and a bit more room. The stock caps are 6 mm X 12 mm at 1 mm pitch. These front caps are 16 mm long and the rear ones 20 mm long with 1.5 mm thick washers. That may be useful, right? The stand off on the rear gib are 1/4 X 1 at 20 TPI. Don't worry about the coarseness of the thread. You don't use them in this set up for adjustment, only support and stiffness.

When you get things this aligned and use a good lube it is just magic what happens. I wish there was some way to show or demonstrate this on a web page.

Marty Nissen's 7x14 mini-lathe project - Fitting the mini-lathe saddle gibs
top view. rear gib

Fitting the Top Slide

I wasn't going to do this next but other items on my list required resources I don't currently have access to.

This was anything but straight forward. A list member guided me over one bump in the road. Jim, I believe it was, noted that when he was working on his slide a bit of material need be removed from the "points" of the doves as they fit together to allow the faces to touch. As the lapping starts to remove height the faces separate. Arrows on the photo below show where and it was suggested that .010" would get it done.

Marty Nissen's 7x14 mini-lathe project - Fitting the mini-lathe top slide

As you can see from the photo I didn't take quite that much.

Before this operation I double checked the parallelism of the doves by measuring across a pair of linear guide rods pirated from a discarded lab device from work. The photo below is a mock up of that operation. Measurements are taken at each end and need be pretty close. This saddle is .0003" and yes you can feel that small amount.

If you remember the height of the dove register was checked earlier when fitting the saddle and was spot on. There is always a risk of upsetting that measurement when lapping anything, if a lot of care isn't taken and constant checks made.

Marty Nissen's 7x14 mini-lathe project - Fitting the mini-lathe top slide

Unlike the saddle, wet/dry paper isn't going to work here. I used dry lapping grits and WD-40 for a carry oil. Brake cleaner and shop towels for clean up. Lay out die to keep track of progress, and a lot of measurement as I proceeded. However before starting the base of the cross slide was blued and check for flat on the lapping plate on 2000 grit wet/dry.

Yes, it was bowed and worked down flat with courser grades of paper and WD-40 until a few swipes across the plate on the 2000 paper would remove all bluing. About a thou was needed to straighten it out.

Once satisfied that it was not only flat but all four corners measured the same thickness the gib, which was already lapped and pirated from the small lathe, was mounted to the saddle loosely.

A liberal spray of WD-40 and a bit of 80 grit was then smeared on three faces, two horizontal and the non-gib angled face then gib adjusted to a medium drag and given about two dozen strokes. As the grit breaks down the gib is tightened and repeated until the majority of the milling machine marks were removed from the horizontal registers. Then satisfied it is disassembled, cleaned with brake cleaner and clean shop rags and repeated with 120 grit, then 220, then 320, then 400 and finally 500 grit.

I should mention I guess that before this operation started a feeler gauge measurement between the upper flat of the saddle and the lower face of the cross slide was taken which measured a "loose" .015". I should also mention that between each grit change a four corner measurement was taken to assure straight and true. This was abandon after the third grit as no change was apparent. End feeler measurement came in at .011" so .003" removed to get her squared up.

After the end of the 500 grit the entire assembly is dismantled and rigorously cleaned with brake cleaner and rags until a white towel comes up clean. Then wiped down with acetone, reassembled and oiled and the slide worked back a forth while adjusting the gib for fit. When you do this you will find that even though you thought you had it spotless the oil will pull more grit from the surfaces. Continue to oil, work it until the oil darkens, clean, and repeat until the oil remains clean. About a half dozen cleanings are required.

Marty Nissen's 7x14 mini-lathe project - Fitting the mini-lathe cross slide
This photo is about half way through the clean and oil stage. You can still see a bit of gray on the right hand track.

Marty Nissen's 7x14 mini-lathe project - Fitting the mini-lathe cross slide
Final four corner check being made with slide centered on the saddle.
All four measured -0 / + .0005 of 1.337" (33.97 mm)

ISO-68 Way Oil was used here as was on the saddle. That may change latter.

Note: The new height gauge? Less than a hundred bucks at Harbor Freight. The Starrett manual vernier is likely more accurate but much harder to read with these old eyes. Quite affordable and has paid for itself already.

This operation took three evenings to complete. Two hours a night and a fair amount yet to go.

You may have noted that the gib side angled face hasn't been touched yet and there is a reason for that, two actually. The first is that as I had a perfectly parallel set of doves I didn't wish to chance skewing them so one, for now, was left untouched to reference the other three to.

The second reason is a much bigger problem and I'll need some time to sort this one out. The original gib from the short machine had been plate lapped just like the instructions say on the Mini-Lathe site. I figured no need to reinvent that wheel. But I had never been totally happy with it as no matter how careful I was I could never get a good match of gib the saddle. It always favored one side or the other, top or bottom.

Just today I figured out why this is and there are two parts to the problem. First the dimples for the adjustment screws aren't dimples at all but three drilled holes the length of the dog point and the same diameter of same. ANY lapping carried out the does not leave the centerline of these holes at dead right angles to the mating face puts a bind on things and rocks the gib, or twist it or bends it depending upon the exact adjustment. It doesn't need any help as it is machined bent, twisted and bowed.

The second is that the gib is not the same height, top to bottom, as the dove slot height and the reason I guess that the adjusters aren't just dimples but the drilled holes must serve as guides as well! Hum, that isn't going to work very well. It is not an insignificant amount at .040". It is also narrower than the slot by just about .030". Thus under adjustment they rock about the adjuster tips and flop either up on down creating the single line pattern I had observed upon disassembly. Placing a light behind the slide I observed at least a 10 degree yaw and no matter how I tried or how tight I made them. I could not get full face contact.

I had a spare new factory gib on hand. I took it and the original to the surface grinder. New factory gibs have no registers for the gib grubs. The original looked flat and looked straight but grinders tell no lies. A few passes and I junked it.

I checked the new one on a surface plate to check for gross dimensional problems and found none so to the grinding table it went. It cleaned up pretty well and not more than .005" had to be taken in any plane to get her squared up, flat and parallel. A quick chamfer on the ends and a diamond stone to knock of the burrs and we were looking good. I set the gib up in the slide assembly with a .035" shim below it and used a transfer punch to mark the locations of the adjusters then spot drilled them just to a dimple large enough to capture the dog pointed ends. Pulled the shim and tried an adjustment. Hum same problem even though this gib was a bit larger and square six ways to Sunday. Okay, I had some .035" X .250 260 brass stock long enough. I made a permanent shim a bit longer than the gib and broke the ends up so that the ends captured the gib then profiled the ends to the gib shape to prevent fouling the dove as it moves. This worked quite well and a blue test showed good contact even though this side was yet to be lapped in. I used some of my adhesive backed sandpaper on the face of the gib and got it much closer and contacting completely from top to bottom but I still have high spots on both ends that needs some work but were going to put that off for the moment.

These factory gibs are JUNK. Gummy and without much memory. You will bend it slightly during adjustment and it will remain bent thus making all your hard lapping work for not. Their hard to grind and even harder to de burr effectively and further more just not the right size to be stable. The brass horseshoe shim is a band-aid until I can make a proper gib for it. Likely A-2 or maybe bearing bronze but certainly not brass. I am a bit surprised how well the shim works though and the idea may make a good low budget band-aid for others.

Marty Nissen's 7x14 mini-lathe project - Fitting the mini-lathe cross slide Marty Nissen's 7x14 mini-lathe project - Fitting the mini-lathe cross slide

06/30/2007
Look at the photo above and compare to the first photo of the top slide project. We're looking at the gib. This is full dimension gib of A2 tool steel I made on the Bridgeport. Full height, full width and full length. It completely fills the slot. The upper photo shows the factory gib made of some soft ferrous material, bent, twisted, bowed and not nearly large enough to fill the slot. And this was a replacement gib which was allot better than that which came with the machine.

A rough blank of A2 was selected from the scrap box and roughed into a rectangle approximately 7 inches long, .250" hight and about .450 wide. You need the extra width to accommodate the 60 degree angles. After squaring and cutting in the angles, which were left fat by about .040" in height and width, the hight was surface ground in to just less than full height of the slide. There is a slight step from the lapping that demands this step. I hang on to the piece with a magnetic chuck. Then the width is ground in to "just" slide in, maybe .0005". One you can get it in the slot the end is squared and fit for length and both ends chamfered 45 degrees, .040" wide. The center and two end original gib adjusting screws and marked with a transfer punch for location. Back in the mill and dimples drilled with a short center drill whose point was just a few thou larger than the dog points. Nice fit!

Next the slide proper finds it's way to the mill. I used a pin gauge mounted in a drill chuck to find the X and Y locations and distances between existing grubs. The distanced halved and the pin gauge traded for a 39 letter bit and holed drilled completely though. Then the bit traded for a 60 degree center point, a Tee handle and 4 mm X 0.70 tap set loosely in place and the center point brought to bear lightly on the end of the tap. This keeps in alignment. Tap and hole oiled well light pressure, just enough to maintain contact is applied with the tap turned by the Tee handle with the other hand. Frequent chip breaking, blowing out the flutes and patiences. Both holes taped they were relieved with a 30 degree (60 included) tool fit in the chuck. This prevents pulling up the first thread.

The two Allen head cap screws had a corresponding 60 degree angle ground on the end of the thread so no dimple was fit to the gib for this. Also maintains a slight upward pressure on the gib. These extra screws made a world of difference. Not only to they lend extra support, which is hardly needed with a gib this stiff, but make nice slide locks as well.

All in all this came out much nicer than I had envisioned. This slide can be ran of the saddle 1-3/4" in either direction before a DTI picks up the faintest indication of displacement of the slide. As it is a 6" slide that is 58.3% travel of rock solid movement. Almost double the factory capability.

I think the head stock will be next. Before I invest a world more work on this project we need to know what the cut in is of the slide. That is to say will it cut flat to a hair concave so a head stock with quill and a jig will need fit up next.

Spindle and Headstock

August 28, 2007
Awhile since the last update eh? Won't even try to explain it.

Now that the saddle is fitted I need to know pretty soon how square it will be to the spindle. To do that I need a spindle and need it mounted in it's final form.

I've decided to emulate the Southbend 10K spindle snout to broaden the options and simplify my tooling requirements. Below is a before and after photo of that project.

Marty Nissen's 7x14 mini-lathe project - A threaded spindle for the mini-lathe

I had some other goals in mind as well. As we will be fitting taper bearings to this I wanted to add proper seals. I've chosen an SKF # 18536, which will require re-manufacture of both current dust covers to accommodate this modification. These are double lip seals 8 mm wide. I suppose some dimensions are in order here.

Thread is a 1-1/2" X 8 TPI fit 2B and is .6875" in length or 5 1/2 threads.

Pilot dimension is 1.509 (-0 + .003) X .1875" The seal area which you'll see in the next snap is 1.875" OD X 11 mm or what was left over of the original spindle flange.

Marty Nissen's 7x14 mini-lathe project - A threaded spindle for the mini-lathe

Thing about the seal area is that it can't have any threading from the turning process. Actually this area should be ground to a 30 RMS finish. I didn't do this. Instead I finished .0015 over size, a hair more than the tool tip radius and hand polished it in to finial dimension. Guess I should say Ron, the machine operator. This was done on a HASS CNC turning center. Set-Tru chuck was used and the spindle indicated in to dead zero from the bearing register. I knew a Southbend was hiding in there :)

Marty Nissen's 7x14 mini-lathe project - A threaded spindle for the mini-lathe

This is the Bison 4" three jaw scroll chuck mounted up.

The result of this is, you will note, is that the "adaptor flange" now replaces the space of the original spindle flange which does a host of very important things.

1.) Shortens the length of the over hanging load.
2.) Reduces the weight of the over hanging load.
3.) Increases the chuck to tail center distance by more than the thickness of the adaptor. (I'll explain shortly)
4.) Allows chuck changes in under 30 seconds
5.) Allows me to use chucks between machines, less tool holding (yes they repeat to under a thou between machines)
6.) Allows use of commercially produced adaptor flanges that can be made into a bunch of other tooling like face plates and catch plates or special fixtures at reasonable cost.
7.) Allows me to move the work in the lathe to the mill or rotary table without loss of reference if it needs to go back to the lathe for a further operation.
8.) Commercial ER collet holders can now be direct fit or flush mount on made on machine adaptors. This also means I can get the saddle and tool to the back side of the work in a thread on ER for other operations without interference or worry of fouling it on the spindle flange.
9.) I can mount a 4" four jaw on a 5 or six inch back plate and make an in place and joint less indexing head!

Marty Nissen's 7x14 mini-lathe project - A threaded spindle for the mini-lathe

Now that explanation. This is the adaptor plate of the chuck unmounted from the chuck and indicated in a 5" four jaw on my SB 10K (which will also fit the Sieg :) Look at the picture above at the distance between the back of the flange and the front of the headstock. Not going to get any fingers in there are you?

As adaptor plates of this thread size are made to fit all machines with this thread they accommodate the longest one thus over a half inch could be removed and in the end it set the face of the flange back further that the original. Not allot mind you but pennies make dollars.

Marty Nissen's 7x14 mini-lathe project - A threaded spindle for the mini-lathe

Spindle thread protector straight off the SB 10K for the 3C collet system.

Now we have a 4" chuck in less thickness than the factory 3" chuck mounted in, on the shorter 10" head assembly on a 14" bed. Anymore
length will come from the tail of the machine.

This modification could also be done with in the Myford 7 platform for those across the pond or down under.

Fitting the Tool Slide

11/20/2007
Finally, a few days vacation and I spent the first one working of the tool slide. Actually my third run at this.

No photo's this time as it would be a repeat of the cross slide in every detail and photo's take up space.

This is a multi part project. As per my usual custom part A was to make a decent gib. Now that I've done several of these it went much faster and with even better results. Someone suggested on my last gib that in the future I use drill bits or plug gauges to find the face width. Done, and is that easier than drawing and calculating it. Thanks who ever that was, great tip. It's also a great way to find irregularities in the dimensions of the slot width.

I started with a piece of material that was much closer in finished dimension as well, another time saver. A 6" length of quarter thick by half wide ground unhardened A2. Having this it went to the surface grinder to finish to the face thickness, that is the thickness from adjuster to working face and to the larger of the two end dimensions which were .001" apart. Next to the mill where I set up a tool vise in the jaws of the milling vise and set with a sine bar to 30 degrees. Machined one side then flipped it over and brought the second side to the height spec required - .002". Cut to length, de-burr and test fit. Supper snug. In fact wouldn't travel the entire slide but expected that as there was a slight taper in the dove as the first measurement showed. Good enough thought to transfer punch the adjuster locations. Remove, set up in the mill again and spot drill the relief's for the adjusters.

Took the lower half of the slide and gave the bottom a quick wipe on the lap plate just to assure no nicks. Laid it up on the surface plate and height gauge in the bottoms of the doves, both sides, both ends. Ouch! The gib side was .0015" taller than the off side but good end to end. Glad I left the gib short .002".

Pair of Thomson rods in the doves and measured the cross difference, .0008" wider at the handle end which just confirmed what the gauge pins told me more accurately.

A piece of sticky back 320 on the top section and a .010 shim on the off side (measured thickness of the paper) and in a few minutes of measure and wipe had both sides the same height within .0002".

I'd made a 60 degree lap on the last gib job. Sticky back on it and worked to offending width problem at the point a bit of blue and touch up had identified as the high spot. Re-measure everything. Looked good. Clean, assemble and lube. Still a bit of stick at the one end and a bit of daylight in the off side gap. Hum. .0002" isn't close enough, but I knew that from previous work on the saddle and cross slides.

A bit of 320 lap powder and light oil in a few minutes we were gold. Clean, lube and assemble again, adjust up the gib. Much better. Not perfect but very, very good. I'll work it more latter.

Perfect has a way of finding imperfect. One of the first modifications I did to the lathe was to fabricate a double thrust ball bearing mount for the feed screw. It's pictured on the front page of my site. It's a matter of blind luck that when fabricating the bearing mount that I left the ID of the bearing bore a couple thou oversize of the bearing OD. Than allows a bit of float that came in handy when the lower slide dove height was lowered to match the off side. Rather be lucky than good any day, eh? Especially sense I used flat head screws and counter sinks thus the block height is not adjustable. Whew, dodged a bullet :) This block is square ten ways to Sunday.

The imperfect part is the feed screw. All assembled and mounted the screw has a tight, loose rotation each half rotation when fully retracted the last quarter of it's length but fine for the last 3/4 of extension. One of two possible problems I see here. Either the thread axis is not concentric to the bearing axis or the screw has a bit of bow in it. Bowed I can fix, off axis is a scrap and remake. Never the less, I'll likely not do anything about it as from a functional standpoint it's fine. It requires no great effort, just noticeable. By default I am now committed to the .040 metric set up and good with that. Zero backlash due to feed screw to mount slop, .002" backlash due to thread to nut clearance, very livable.

I mentioned at the beginning that this was my third run at this. The first got derailed when I found the doves of the original bottom half of the slide so far out of parallel as to be un-fixable. I bought a new lower from LMS to the JWE design. Ground in a factory gib and did a bit of light work which served the machine until it was dismantled for this project.

That pretty much finishes the gibs on this machine, saddle, cross slide and tool slide.

So what was the end result? Placing a DTI mounted on the bed and indicator tip on the tip of an indexable tool mounted in my A2Z QCTP and applying 10 lbs of downward pressure to the tool tip netted under .00015" total deflection with all slides centred. This test with my best adjustment previous to refinement netted about .005" deflection. Thats a 33 X improvement!

As the gib adjusters are on closer centers than the cross slide was I'm electing for the time being not to add the additional adjusters nor lock screw. A minor item to fix if needed latter.

I think this part of the goal accomplished!