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I pulled the headstock and pressed out the spindle and bearings today. My original plan was to make an elaborate expanding mandrel. This was mandated by the need to press the bearings out of the housing, but having to clear the 25 mm bore to do it. But happily I woke up this morning with a simpler idea. I turned some bar to about 27 mm to clear the 28 mm spacer and 25 mm bearing bores. I then cut off a 2-3 mm slice and cut that in half. That let me drop the 2 halves through the bearing bore and then set them on top of the inner races. I've included phtots of the half disks and with them in place prior to pressing the inner races out. I then used a socket and extension to press on the half disks and push out the outer cones and the plugs. To remove the outer races I used another socket and extension. The last photo shows the housing with the bearings removed and makes clear why both had to be pressed outwards from the opposite side. The headstock housing appears to be undersize, but I'm not confident measuring it with telescoping gauges, so I've ordered a 0.0001" dial bore gauge. After a lot of searching I found that the spindle and housing tolerances for ABEC 7 bearings are the same as the bearings. In the case of the 7205C-P4-DGA bearings that's +0/+0.0002" and +0/-0.0003" respectively. Aside from being *very* difficult to measure that closely there is the question of how I'll remove the metal to bring them to tolerance. However, I'm very happy I don't need to plate the headplate bores. I measured the spindle journals and they are 0.0001" and 0.0002" oversize based on 5 measurements of each journal. After investigating tool post grinders, I've decided that is too risky for such small cuts. Present plan is to flatten the face of a small corundum sharpening stone and glue it to an angle plate, mount it on the compound and then press it against the spindle while it is spinning between centers on my 10 x 20 Clausing 4902. That will be *very* slow which in this case is a big advantage. I'm allowing myself a tenth of overrun. The housing bore is more difficult. Present concept is to make an expandable plug with 220 grit wet or dry paper and just turn it by hand or perhaps electric drill to open up the bores. In the event I fail on the ABEC 7 bearing installation, I may simply make tapered bronze bearings and lap them to the outer races of the OEM 30205 taper roller bearings. That's the traditional bearing for an instrument maker's lathe as it is the only bearing that has *no* rotating errors. You rough out the taper and then lap the bearing to the race. My 4902 has plain bearings, but they do have the downside that you *must* be attentive about oiling them often or fitting large oil cups. So the adventure continues. There are high spots at the exterme ends of the front way. As the ways are ground, I'm going to glue some 220 wet or dry paper to a plate which has been ground on a surface grinder and sand them down a tenth or two. Have Fun! Reg

Here's a photo of my setup for testing the mill spindle. Same MT 2 test bar. At 3 " from the spindle face I am clocking ~0.0002" TIR! The spindle is using skateboard bearings! These are only ABEC 3, but the skateboard crowd is big into "ABEC 7" except that the very low price suggests that they are not. An ABEC 7 from Boca Bearings is $150 each. I have found ABEC 7 from VXB for <$50

I'm doing a review of the Grizzly G0937 combo lathe/mill on the [email protected] list. The purpose of this post is to document how I'm testing the machine. I'm using a ground between centers MT 2 test bar from India which I bought on ebay for a very nominal price. It has proven to be very accurate. The photos show the two basic test setups. The bar cantilevered from the spindle and with the end supported by the tailstock using a dead center. I made 4 passes measuring vertical and horizontal deflections and TIR for both setups. The rings are at ~ 1" spacing from the spindle face. I'm using a 0.0001" test indicator. With the bar supported by the tailstock TIR is ~ 0.0001" from end to end. I clocked it 0.0004" low at 6", however, the tailstock ram has about 0.001" of play in the tailstock casting, so that number is somewhat suspect. I'll retest after I eliminate the ram play. I've adjusted the tailstock position as best I could, but the design is very difficult to get where you intend and keep it there when tightening it up. It was actually within a few thou over the length of the bar which is quite reasonable for an "as shipped" condition. With the end unsupported there is 0.0005" TIR at 1" from the spindle. It is offset to the rear 0.0033" at 8". There is 0.0010" TIR at 6" and 0.0010" droop. This is a 1' 2" axial error of the spindle relative to the axis of rotation. The spindle bearings are 30205 taper roller automotive front wheel bearings. I plan to replace the bearings with angular contact ABEC 7 machine tool spindle bearings to see how those perform. But truth be told, the machine is already more accurate than my skills as a machinist can fully exploit. But I'll enjoy learning how. I don't have an independent means of testing the bar, but I have observed no indication of any measurable error in the bed which I find quite astonishing for a ~$1250 machine including tax and shipping. It inevitably has shortcomings, but the ones I've identified so far are pretty simple to correct. Have Fun! Reg BTW The 7" x14" mini-lathe still sits rather unloved waiting to be reassembled after being subjected to the tender mercies of UPS :-( Between the aggravation and the vicissitudes of old age I just haven't been motivated to work on it. However, I bought quite a bit of tooling for it, so that will happen eventually.

I got one of these from another seller. After struggling with my various indicator holders I thought perhaps I should mount the indicator on the milling attachment table. https://www.ebay.com/itm/Mini-Lathe-Milling-Attachment/363243067082 I find myself struggling to decide how to mount it. I don't want to drill holes in the mini-lathe and then discover I got it wrong. I considered mounting it in place of the tool post, but the range of Z axis motion is then quite small because of the height of the top slide. If I mount it in place of the compound, I improve the Z axis range of motion but lose X axis movement. The other option I can think of is to mount it directly to the cross slide, but then I lose the ability to rotate around the Z axis which the first two schemes provides. While I could make a pivot hole in the cross slide, I wouldn't be able to lock the angle securely. The only other approach I can think of is a 1/4" steel plate that attaches to the cross slide and has a pivot and arcuate slot to take two screws using the holes in the base of the vise. I'm leaning in this direction because it seems the simplest approach. Has anyone tackled this? What did you do? Have you seen a good discussion of the pros and cons of different solutions? Or is this one of those, you have to have more than one mounting setup problems? I don't expect it to be a replacement for a mill, but it has the potential to be useful for some tasks which would require either a collet fixture or a pair of centers mounted on the mill table such as cutting a Woodruff key slot in a shaft. Having seen the many accessories for the Myford 7 I'd like to replicate some of them on the mini-lathe. My current need is to be able to correctly place the indicator on the diameter of the test bar even if the bar is not parallel to any part of the bed. I think I did OK on the headstock, but won't be sure until I get a 3 MT dead center. Have Fun! Reg

The rack is 16.5" long. The carriage has a maximum travel of 15" when the tailstock is at the end of the bed. But when I get close to the headstock, the gear and rack disengage about 1/2" from the headstock. It's easy to reengage it, but annoying. It's also a potential nuisance as I plan to use fixture plates which puts me closer to the the headstock than than a chuck does. The milled surface for mounting the rack extends to the left of the rack by slightly more than 1/2". This has me contemplating moving the rack over by drilling and tapping new holes in the bed. In either position the extra holes will be covered by the rack and only visible from the rear of the lathe. So it seems a pretty innocuous modification. You can, of course, use the top slide to move the tool farther towards the headstock without disengaging. But it seems to me the rack and gear shouldn't disengage in any carriage position. Is there something I'm missing, such as a reason to disengage the hand wheel? As there is no gearing to drive the rack from the leadscrew I can't see a reason to allow it to disengage. If there were, it would prevent crashing the carriage into the headstock under power feed. But on these the power feed is always done by the leadscrew threads. Do other mini-lathes disengage the rack near the headstock? Reg

Well, at least this is why mine isn't. It's probably a common defect, but there are so many ignorant bodges that attempt to fix the problem with shims that actual standard lathe building practices have never appeared in any mini-lathe discussion I've read. The problem here is that the flat portion of the headstock to the left of the vee needs enough metal removed to let the vee fully mate. IIRC I measured it as 0.003" using feeler gauges on both sides of the vee and a bit of trig. So this is a few hours of bench work with files, scraper and surface plate to fix. Easy to do, just time consuming if you're not proficient at it and have to feel your way along for the first time as I shall have to do. Though I do have the advantage that I regularly practice my bench work instead of setting up machine tools for a trivial task. It's a finger tip skill just as is trowel work or playing a musical instrument. You've got to stay in practice. One could bodge it by inserting a shim along the side of the vee, but that would not correct any lack of spindle parallelism in the vertical plane. So a 2nd shim would be needed and probably another to fix the errors that introduced. Have Fun! Reg

I decided I'd finally bought enough electronics test gear and so I unpacked the mini-lathe to start work on it again. The hiatus proved useful as I completely rethought the 3 point mounting system for the lathe and this should work much better. The first photo shows the parts. It's 4" and 6" pieces of 1" x 1/4" HRS, three 3/8" swivel feet and three 3/8" bolts. I still need nuts for leveling the feet. Also I've not yet marked out and drilled to bolt the HRS to the lathe. The 2nd photo shows the supports assembled (minus nuts) The third photo shows the lathe set up on the legs. By using 3 points and ball joints at each support, there is no way to apply twisting force to the bed of the lathe. For someone working in a cramped space, the bench top could have shallow counterbores to take the swivel feet. That would allow storing the machine easily, but still having it securely mounted to the bench when in use. All without concern for whether the lathe is actually level, etc. Have Fun! Reg

To start this thread you should really start reading the posts here as this is where it started and provides the context: /g/machine-tool-rebuilding/message/13 A horizontal force on the gib will produce a force normal to the surface and a downward force. I don't see an issue with the gib being in contact with the base of the male dovetail. That's a precision surface. The problem is that if the gib can't preload itself against the gib screws using the downward force, you don't know where the screws will seat in the gib bores. Yes, you can put points on the gib screws but this is self-defeating as it creates high stress at the screw seats so they deform quickly with use (confirmed, I tried it). Well then you say, use a ball and socket shape for the screw and bore, or make the screw tip and bore exactly the same diameter, or use a conical tip going into an undersized bore so that finally, we will have a gib-screw interface which seats correctly every time and never deforms. But no, you still have a problem because the screws themselves have play in the threads and move around easily under stress. So maybe you fix that somehow, but also did you consider that the screws tips may not be perfectly concentric, and so adjusting them always introduces errors? So then you find a way to fix that. Then what you're left with is a very finicky mechanical system where numerous small things all have to be working perfectly and is basically impossible to maintain in optimal condition and is always degraded after a repair. The form taken by this error is also particularly bad. What happens is that when horizontal force pushes the gib against the dovetail, defects in the system flip a coin to determine whether the slide is deflected down against the slide or up away from it (or both alternately during a cut like a toggle switch). The latter is bad because the compound suddenly becomes very compliant. This means that if you clamp the gib screws in an attempt to rigidize the compound, you may actually end up pushing the slides slightly apart, and then you lose accuracy as well as rigidity. I considered this stuff when I wrote my webpage. In my solution the preload between the gib and screws serves not only to rigidize the gib but to stabilize the screws and screw seats. Preload here provides us with room for error, room for wear in, and a system that doesn't need to be too reliant on everything going well. BTW I found confirmation that there should be clearance between the gib and the upper surface of the female dovetail in a short article about making gibs in one of Guy Lautard's "Machinist's Bedside Reader" volumes. On reflection, that makes sense. You would not want the upper face of the gib to bind against the clearance face of the female dovetail. That requires that the lower face of the gib be forced into contact with the horizontal surface of the male dovetail I'm interested in this article. A solution would be to shim the gib enough that the upper left corner is below the male dovetail corner. Another solution would be to make a groove in the left face of the gib to provide clearance around the dovetail corner using a Dremel mounted something like a router. Anthony, as you have done a good bit of work in this area before, would you mind posting a bit about measuring the deflections of a dovetail way in various positions? The real focus here should be, "How do you determine what the problem is? How do you measure it? How do you fix it." With links to projects-in-metal for how to make things you don't have. You determined that the gib was the problem, I simply accepted your premise as I had experienced it. I posted some pictures of my measurement setup. I wrote a webpage explaining how to fix it. I didn't have to build anything to do the measurements, I just used a random pipe, spring scale and tenths indicator. Depending on the state of your gibs, fixing it might be as simple as adding a shim. I was mainly concerned about sideways forces on the cutter, either from facing or trepanning or from the cutter being extended past the edge of the cross slide so it acts as a lever. I quantified this by using a tenths indicator to measure the movement between the slides close to the gib. I put a pipe over the toolpost mounting bolt and used a spring scale to apply a known force and extrapolated the force on the gib according to the ratio of lengths from the gib and scale to the fulcrum which is the left side of the cross slide. You can see my setup in this picture and I also included the force deflection chart.

Yeah, the old base was pretty bad. I think it came very roughly scraped and concave so that it might sit flat on the bed ways. The front face of the registering key on the top was the same way, and combined with the divot from the set screw on the back of the key it was difficult to adjust. But my new one and my old one have the same size and shape base. They’re both fitted to the 7x16 bed now, and I copied the 75° dovetail and gib from the new one when I redid the old one. They both clamp the same, though with thicker plates and fitted so they don’t tilt or skew as they tighten. The captive left-hand threaded clamp handle on the new one works okay but I got used to keeping track of the wrench. I rebored the casting and made a new barrel for the old one, and it fits as well as the new one. It’s 22.5mm diameter instead of 25mm but it isn’t slotted or bored out for a Morse taper. The new barrel made a big improvement, but the old tailstock is still flexible compared to the new one. Once they’re clamped in place, I’m not sure what to point to other than the structural design of the casting. It looks like newer, non-nesting cam lock versions shown on the lower price lathes on Amazon and Ebay correct that. Looking at pictures of other, better small lathes I think it’s interesting they seem to have changed from tailstocks like my new one where the barrel is longer than the main casting to ones with shorter barrels that work more like the old one used to.