# HF 7x10 Mini Lathe Compound Dial Binding



## NF6X (May 18, 2020)

I have an older Harbor Freight 7x10 mini lathe, model 33684, which I allowed to get rusty and decrepit. I'm now fixing it up and upgrading it with lots of fun stuff from Little Machine Shop: metal gears, quick change tool post, carriage lock and stop, 4" 3-jaw chuck, holder to use a Proxxon tool as a tool post grinder, etc.

When I crank the compound slide inwards, the dial binds against the bracket supporting the lead screw, and it holds still while the screw turns. Looking at how it's designed, I don't see how it could do anything else except by dumb luck. It sure looks to me like the dial serves as one of the thrust bearing surfaces when cranking inwards, with the little spring, crank-to-dial friction, and dial-to-bracket friction all competing over who gets to turn the dial. My cross slide's dial does not seem to be binding like that at the moment.

Am I missing something here, either physically or conceptually? I can imagine that adding a radial thumb screw in the dial to clamp it to the lead screw might make it slightly less awful, but it sure seems to me like the dial shouldn't be playing any role in bearing the feed screw thrust load. I wonder if anybody has re-designed the feed screw thrust bearing scheme to work better.


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## royesses (May 18, 2020)

I drilled and tapped the dial for a set screw that I use to tension the curved flat spring in the dial. Adjusted until the dial only spins on the lead screw when I want to zero it. I installed a needle thrust bearing with its 2 hardened washers in the bracket and made the depth of the bore in the bracket deep enough to keep the dial and bracket about .002" apart so they never touch each other touch each other. I think the needle bearing is this check the measurements on your lead screw and bracket to make sure:








						AXK1226 THRUST NEEDLE ROLLER BEARING WITH TWO WASHERS 12mm X 26mm X 2mm FRD235  | eBay
					

YOU ARE BUYING AN EXCELLENT QUALITY THRUST NEEDLE ROLLER BEARING.



					www.ebay.com
				



 It is a poor design from the factory.

Roy


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## royesses (May 18, 2020)

Here are the LMS instructions for mounting the lead screw and pillow blocks on the 16" extended bed. They may help you getting this all adjusted.

Roy


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## NF6X (May 18, 2020)

Adding a needle thrust bearing sounds like a nice improvement. What keeps the flat spring in place under the set screw when you turn the dial to re-zero it? I'd think that the flat spring would be more inclined to stay put with respect to the lead screw rather than staying put with respect to the dial.


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## royesses (May 18, 2020)

That spring is stuck between two washers in its bore so it can't move out of place. You can order another spring from LMS and put them in forming a complete circle so they will always have the extra tension on them. That's how I did it.

Roy


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## NF6X (May 18, 2020)

I'll try bumping around the pillow blocks to see if I can get them aligned better. I can't help but wonder whether I might be able to do better than plain iron bearings with no oil holes for the lead screw. If I understand correctly:

The lead screw axis needs to be aligned well with the path that the centroid of the half nuts follows.
Axial free play on the lead screw should be minimal, and the machining forces will turn into thrust on the lead screw against one pillow block or the other depending on direction of carriage travel.
There isn't much radial load to deal with in the pillow blocks.
Radial free play on the left side should be minimal, both to position the lead screw with respect to the half nuts in the apron and to keep the drive gears meshed nicely.
Radial free play on the right side is less critical because it's just keeping the lead screw from flapping in the breeze too much.
Thus, it seems to me that I might safely increase radial bearing clearance a tiny bit on the right pillow block if I can't eliminate the binding by bumping around the pillow blocks, but I probably want to leave the left block's radial bearing alone and I don't want much axial free play at all. Does that make sense?


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## royesses (May 18, 2020)

I also bored out the other side of the compound bracket for I think 1mm ball bearings and used 24 or 25 bearings. They ride against the flange on the lead screw and the bore I made 1mm deep so the bearings are captured. I lubed them with 65% moly containing grease. The compound is smooth as silk in both directions now. This was done in 2017 and it is still going strong. I ordered spare parts from LMS first in case I screwed up, but I accidentally got it right on the first try. It is so smooth it is scary.

Also one of the most useful upgrades is the LMS extended cross slide kit. Probably the best mod I've made besides the 16" bed and tapered roller bearings on the spindle. I also made tapered gibs for the carriage and that is a tie for the best upgrade. Got to love LMS, they have everything a minilathe could ever want.

Roy


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## NF6X (May 18, 2020)

royesses said:


> I accidentally got it right on the first try.



LOL! I love it when I accidentally forget to mess things up.


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## royesses (May 18, 2020)

When I added the extended bed I also drilled the pillow blocks for oil fittings:








						Oil Fitting, 6 mm 1655
					

Mills, Mini (X2/SX2) Replacement Parts 1655 This 6 mm oil fitting is used on the lead screw brackets on the mini lathe as well as the tailstock of the...




					littlemachineshop.com
				



I slid a piece of windshield wiper hose (1/8" or 3/16") over the end of my oil pump can to lube the pillow blocks. The rubber hose extends about 1/6" from the end of the oil can spout so it is compressed when I push the spout down onto the oiler. This lets me give a good shot of oil to the lead screw without making a mess.

Roy


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## NF6X (May 18, 2020)

My pillow blocks don't have oilers, or even plain holes. Just the ability to hose against the exposed right end of the shaft. I ought to at least drill a hole in the top of each one to drip in some oil.

Derp. I missed where you wrote that you drilled them for oilers.


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## NF6X (May 18, 2020)

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.


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## royesses (May 18, 2020)

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


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## NF6X (May 18, 2020)

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.


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## royesses (May 18, 2020)

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


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## NF6X (May 18, 2020)

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.


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## royesses (May 18, 2020)

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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## NF6X (May 18, 2020)

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.


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## Ken from ontario (May 19, 2020)

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


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.


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## homebrewed (May 27, 2020)

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.


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## homebrewed (May 28, 2020)

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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## NF6X (May 28, 2020)

It occurs to me that even if I made perfectly matched replacement pillow blocks, I might still need to account for misalignment from their mounting surfaces on the lathe base casting not being coplanar and parallel to the ways.


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## homebrewed (May 28, 2020)

NF6X said:


> It occurs to me that even if I made perfectly matched replacement pillow blocks, I might still need to account for misalignment from their mounting surfaces on the lathe base casting not being coplanar and parallel to the ways.


Yep.  Unfortunately, in order to mate with a nonperfect lathe casting it will be necessary to make an imperfect pillow block  .  But there are reasons why shims have been around for a long time.


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## NF6X (May 28, 2020)

So true!


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## jaek (May 28, 2020)

The lathe seems to work fine with the right side pillow block screws still loose, if you're looking for the easiest fix possible...


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## Firstram (May 28, 2020)

When I was faced with the same problem, I cheated and used Timesaver to lap them. Once the lead screw was smooth, I made a bronze thrust washer to take up the end play. Kinda hack but it's still smooth 9 years later.


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