Mini-lathe headstock modifications

February 2010

Mods on the headstock, as well as with the mini-lathe bed, were the ones that took more time to be planned. The idea was to make all modifications on the headstock at the same time, being sure that one will not turn another more difficult to make. To plan everything, the headstock was fully disassembled once to make all necessary measurements. Then assembled again to make all necessary parts to perform all modifications.

Headstock metal gear

Mini-lathe heastock metal and plastic gears

A few years ago, having the mini-lathe for a couple of months, got the spindle HI-LOW gear broken. Thinking now about the causes for the broken gear, guess it may have been the excessive loose fit on saddle, cross-slide and compound combined with poor cutting tools. Now decided to get that gear on metal, to avoid the need of disassembling the spindle again if another plastic gear get broken.

Due to my concern of keeping the lathe as silent as possible, and after reading complains from 7x12minilathe group members about the noise that the full set of metal headstock gears make, decided to do it the Micromark way. The spindle gear on metal keeping the plastic countershaft gear. This way if something goes wrong someday it will be the countershaft gear that can be damaged, and that one is fairly simple to replace. But I don't expect that much for the plastic gear to get broken, as they have been proving to be very resistant. So my decision was to keep one silent plastic gear.

This time ordered a spindle metal gear from LMS. The one I received is Indian made and after checking that small size differences wouldn't cause any problem, used a small file to remove all the sharp edges from gears teeth to prevent excessive wear on the plastic gear. While doing it, it's easy to feel the difference only by touching it with fingers. Then, placing 400 grit paper around the small file, smoothed every gear teeth.

Unfortunately, found later that I forgot to check dimensions of the bore ID. The bore is undersized and the gear don't fit on spindle. As only found it having already the headstock disassembled, had to use a Dremel type tool to enlarge the bore for the gear to fit on spindle.

Arc Euro Trade in UK also sells spindle metal gears. As far as I know, by this time the ones they sell are in three separated parts. Two gears and a spacer.


Mini-lathe heastock plastic gears after over 440 hours of lathe work

On my early mini-lathe days, have mounted on the controller box a time counter I was having new and with no use for it. Only now I found a good reason to have it there. As preventive maintenance, I will replace the intermediate gear on headstock for a spare one I was having here. The old one have made over 440 hours of lathe work, as you can see on the time counter, and it is dirty but in good condition. This info will be fine to check if the metal gear will wear the plastic gear too soon.

Spindle tapered roller bearings

The deep groove rubber sealed ball bearings that came on the lathe are nothing but a cheap bad solution for a lathe spindle. Deep groove ball bearings are intended to work only with radial forces and not with axial forces. Also there is more internal clearance on these bearings that should be present on a lathe spindle. My choice here was for the common replacement for tapered roller bearings and ordered two SKF 30206 (30x62x17.25mm).

Mini-lathe ball bearings and taper roller bearings dimensions

Figure shows differences from the standard deep groove ball bearings and tapered roller bearings. All dimensions are in milimeters. Differences on dimensions have been considered when preparing this mod to make new spacers with the correct dimensions, bearing seals and new bearing covers.

Also decided to replace the countershaft bearings. Instead of using here rubber sealed ball bearings, decided for metal shielded bearings (SKF 6001 ZZ). Metal shielded bearings are more efficient as rubber seals have higher friction. As an example, for this bearing size (12x28x8mm), SKF data for limiting speed is 17000rpm for the 6001 2RS (rubber sealed) and 30000rpm for the 6001 ZZ (metal shielded). Loosing motor power due to friction on the countershaft bearings seals is always undesirable, and that made my decision.

Headstock disassemble and assembling instructions

Arc Euro Trade has a good guide with instructions for the tapered bearings mod. Very useful and full of instructions on how to disassemble and assemble the mini-lathe headstock. For the spindle nuts, it is a good idea to make a set of spindle nuts wrenches.

Bearing seals

Mini-lathe spindle tapered roller bearing sealings

For the spindle tapered roller bearings have made seals from automotive jointing material. Seals were made after calculating dimensions of the bearing housings on the headstock and bearing dimensions. The jointing material used is 0.7mm thick, and each seal was made in three parts in order to make clearance for the bearing. As new bearings are 1.25mm thicker than the original ball bearings, two 0.7mm parts of each seal are actually spacers.

Seals have been made by using a compass cutter, a great tool for this kind of job. After measuring the distance from the center of the spindle to the center of the countershaft, marked this distance on the jointing material in order to know where the center of the compass cutter should work. The first cut make the clearance for the countershaft bearing, the second cut makes the seal OD and the last one the seal ID. Seals ID's are different for the front and rear bearing, accordingly with spindle and rear spacer dimensions.

4" / 100mm spindle upgrade

On the same week I got the bearings delivered to my door, found that Realbull has now a new version of the 7x14 mini lathe with a 550W motor and a spindle for 4" chucks. The 550W motor is not new on their lathes, but I think the new spindle is a huge advantage. And, has Realbull 7x12" and 7x14" mini lathes have the same headstock, it will fit all 7x12" lathes.

Having the mini lathe a 20mm spindle bore and a swing over cross slide over 100mm, the 4" chucks are the ideal chucks for it. A 4" chuck can hold up to the stock size that can be turned over cross slide and the chuck 25mm bore enable full use of the mini lathe spindle bore. A 3" chuck may be enough for many work holding but their 16mm bore is very limiting.

By mounting a 4" chuck directly on the mini lathe spindle, without the need of a adapter plate, not only will save bed length as will reduce chuck overhang. Moreover, tightening the chuck mounting nuts on a larger spindle flange will surely make chucks easier to mount. All these advantages are just too much to be forgotten, and ordered one of these new spindles from Amadeal in UK. They also sell on ebay. Cost was a bit over the price of two adapter plates for 4" chucks.

Mini-lathe headstock, the original spindle and the 4

Here are both spindles. I found the new one to be much better finished than the older. Chuck fitting surfaces on flange are very well grounded, as well as bearing seats have been precisely grounded to the right dimensions. Bearings fit on seats very well. They have to be pressed, but not excessively. And it's easy to add and to remove preload.

The new spindle has seven holes on the flange. Six are to mount 3 and 4 jaws chucks, as on the previous spindle. The seven hole is to access the bearing cover screws, that are now not accessible through the chuck mounting holes on flange.

Mini-lathe headstock, spindle and 4

Now, about how easy the new 100mm - 4" spindle makes changing chucks, here it is a photo before the mod with a 4" chuck and adapter plate. Of course it is hard to get to the little M6 nuts.

Mini-lathe headstock, 4

Here the same 4" chuck on the new 100mm - 4" spindle. The flange is higher than the headstock casting, there is more space between the headstock and spindle flange and nuts are larger M8, easier to catch with fingers. I have measured 17.62mm from heasdtock to flange, the space used for fingers to get the nuts, and it really makes changing chucks much easier.

Besides the larger diameter of the flange, this is the only difference in dimensions from the original 80mm - 3" spindle and this new one. Have compared all the other dimensions with the Sieg spindle dimensions (LMS drawing) and all are the same. This may be good news for Sieg mini-lathes owners, as now they also can upgrade the lathes to a 100mm - 4" spindle.

Headstock gears lever

I'm also trying to make the lathe more operator-friendly and, with the motor speed reducer mod, will be changing headstock gears ratio a lot more. Never found to be a good idea to have the gears lever on the back of the headstock, and so it was now relocated on the front. The previous hole on back for the lever was filled with JB Weld and the headstock was drilled in front for the new lever. A collar is bolted to the headstock with two M3 screws and it has a straight point setscrew that fits a groove on the lever shaft. This is to prevent axial movement of the shaft. It has on front three dents for the lever to stop in position.

The second collar is secured to the shaft with a setscrew. A setscrew in front pushes a spring and a ball against the dents on the first collar, to make the lever to stop on gears positions.

I'm also making a new controller box, and the lever shaft was made with dimensions to pass through the inside of the controller box.

Mini-lathe headstock, 4

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