HF 7x10 Mini Lathe Compound Dial Binding

Hmm. With all four lead screw pillow block screws loosened, the lead screw turns easily. Tightening the mounting screws for either pillow block increases the lead screw friction, and then tightening the screws for both of them increases it still more. I wonder if my pillow block have bores that aren't parallel to the planes of their mounting pads, have different bore heights, or some other such weirdness.
 
Yes it could be any of the above. Also the lead screw could be slightly bent.You might need to make a couple of shims to try and get the pillow blocks in true alignment. I would tighten the left side pillow block screws with the half nuts engaged then slide the right pillow block on and measure any gap between it and the bed. Then make some shims to take up the space. China doesn't have the best quality control. They use a bigger hammer when thing don't fit. There are no factory rejects.

Roy
 
I'll see what I can figure out without proper equipment for this kind of metrology. First step is to get the lathe working well enough that I can start using it to make its own parts for the next step, such as a new spacer for when I replace the spindle bearings. I have a hunch that they deliberately used a plastic spacer, figuring they could just crank down on it and then let the heat from excessive bearing preload soften it. Self-adjusting bearing preload. :)

But I plan to turn a new spacer out of aluminum before I replace the original spindle ball bearings with conical roller bearings, and also upgrade the plastic gears inside the head stock at the same time. I just ordered a 4" 3-jaw when I realized that the jaws on the original 3-jaw can't be reversed, and won't be able to grab the chunk of aluminum round that I'll make the spacer out of.
 
I too run a 4" chuck. I think you may be correct about the spacer. I used the plastic one when I replaced the bearings, but I might make an aluminum spacer next time I grease the bearings. If I ever remove the headstock again I'll also check alignment of the gears and make spacers as needed to get them aligned. I've had all metal gears since the first month I owned the lathe. No stripped gears to worry about.

I think that as long as you get lead screw to spin freely and not bend when engaging the half nuts you will be good to go. There are so many mods and upgrades for these little guys that you can spend all your spare time improving you mini lathe.

Roy
 
Yeah, I have mixed feelings about putting too much effort and expense into this mini lathe, vs. putting effort and expense into my much bigger 12" Atlas-Clausing, vs. just getting a lathe that's already good and doesn't need restoration and/or upgrades. :)
 
If I had the room I'd have a 12 or 14 inch lathe. But at my age I'll make do with a minilathe and mini mill. These little guys can get expensive in a hurry, but they will never be rigid enough for large work. They are very useful though and a lot of fun.

Roy
 
My immediate projects for this one are making new capstan rollers for DEC TU58 and HP 85 tape drives. I think that tuning up my little 7x10 should make it pretty handy for small items like that, even if it's not nearly as nice as my big old Atlas Clausing will be if I get around to fixing it up.
 
royesses said:
If I had the room I'd have a 12 or 14 inch lathe. But at my age I'll make do with a minilathe and mini mill. These little guys can get expensive in a hurry, but they will never be rigid enough for large work. They are very useful though and a lot of fun.

Roy
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I am in the same boat as you Roy, have chosen my mini mill and mini lathe for the very same reasons (lack of space for bigger machines, not having the capability to install/move heavier tools), could have got a decent Bridgeport mill(plus some tools) almost for the same as what I've spent on the mini mill, that also goes for my mini lathe, small machines in general get bashed often mainly for lack of accuracy and rigidity but the fill a need for users like me , I always tell the potential new buyers to fully understand the limitations of the tool or equipment they are about to buy, it might just save them money and a huge disappointment.
 
I've been thinking about adding thrust bearings to my lathe's leadscrew as well. I don't think it will be necessary to do it for both ends -- after all, if one end is captured by the bearings/pillow block, the other end isn't going to move, either. I'm mulling over making a pillow block or modifying the one I have. I probably will make a new one so I have a back up in case it doesn't work out. Aluminum should work just fine for this.

Something to keep in mind with regard to using needle thrust bearings is that they are not self-centering (the washers are flat). The ones with balls have grooved washers so the bearing race is forced to be concentric w/regard to the washers. I'm having difficulties with a Y axis thrust bearing mod I did for my mini mill and I think that is the source of my problem -- the needle thrust bearings I used can't prevent the feed screw from dropping down and rubbing on the bearing block so it squeaks (very loudly) when the handcrank is turned. It always comes back despite lots of grease I put in there. I bought some of the grooved thrust bearings as replacements but have some work to do because they are thicker than the original needle bearings. Deep-groove bearings might be an option as well. If taking that approach I'd stick with the deep groove style because applications like these can place a significant axial load on the bearing.
 
I neglected to mention some things that I DID do regarding a lead screw/split nut alignment issue I had. I did the full alignment procedure that's been mentioned above and still had a pretty significant misalignment problem. One issue was that the alignment always shifted when I tightened down the screws that attach the apron to the saddle. I found that the bottom faces of the original screw heads were rounded so the screws always moved the apron around -- so each screw was centered in the saddle's slotted holes. Buying better screws fixed that problem, but there still was some residual misalignment.

I don't have any photos of what I did next, sorry about that. If there's interest it would be fairly easy to at least re-create the setups I used.

The next thing I did was to refine the right-hand pillow block (my observations showed it was the main culprit). I made sure the surfaces underneath the mounting screws were flat (using my mill), and I also milled the bottom of the pillow block to make sure it was flat. To ensure the bottom plane of the block was exactly parallel to the borehole (where the leadscrew goes), I made a mandrel to hold the pillow block and used my lathe to face both ends of the block. This gave me two sides that were parallel to each other and exactly perpendicular to the borehole. I used those reference surfaces to set up the milling job for the bottom of the pillow block. I had thought I would need to add some shims to get the correct alignment but lady luck was in my favor that day -- I removed just the right amount to get the alignment right! That was a first, for sure.
 
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