HF Mini Lathe question

[onthefence777]

So a while back I bought a HF 7x10 Mini Lathe on craigslist. It was in pretty rough shape, missing all change gears, ways were a bit rusty, power feed did not work, and the carriage and crossfeed slide had a TON of play in them. I went through it, got all the surface rust off of the way and got it in pretty decent overall shape. Read up a lot about it, and got all the gibs adjusted very nicely, performance was drastically improved.

But I still was getting quite a bit of runout on the chuck. The chuck is by no means precision, but with the jaws in the correct orientation, it doesn't seem like it was coming from the chuck. Since the runout became apparent when I was putting pressure into the work, and it was accompanied by a rough bearing noise from the headstock, I figured it was the headstock bearings.

Since I was tearing down the headstock anyways, I decided to upgrade the regular roller bearings for the angular contact bearings at littlemachineshop.com. Since the angular contact bearings are slightly wider than the roller bearings, a spacer had to be turned down to make up for the difference. I bought a spare spacer, and a neighbor that also has a HF mini-lathe let me turn it down on his lathe, and use his press to remove/install the bearings in the headstock.

So I got it all back together, and voila! Chuck run-out was basically entirely gone. It seemed to run WAY smoother than before, and so after the brief "break in" recommended (spinning at slow speeds for a couple minutes, increase speed in increments for a few minutes) I tested it out by doing a facing operation with spectacular results! I then began to do a turning operation, not a big cut at all but not a finish cut either. Well after less than 15 minutes of operation the motor started groaning and turned very slowly and then wouldn't turn.

Upon removal of the motor, I discovered that the motor brushes were pretty well worn out. I have new motor brushes to install. I am hoping that that is the only problem with the motor.

But this is where my question comes in - I am wondering if I didn't turn down the spacer that puts preload on the headstock bearings enough. When I turn the chuck with very slight effort, it turns very smoothly with no resistance, but instantly stops if I stop turning it - I.E. it does have drag on it. I wouldn't call it "tight", but it definitely doesn't free spin. Is it possible there is too much pre-load on the headstock? Should it spin freely? Is it possible that this placed too much load on the motor, and consequently wore out the brushes? Or was this just a coincedence?

Any advice would be greatly appreciated. I am going to start swapping in the new brushes tonight, and see if hopefully the motor is ok.

 

[onthefence777]

Installed the new brushes and wired it up the motor before installing, and it does run

I do get the feeling that there is just too much pre-load on the headstock however, but I'm a newbie to machining so

 

[mbshop]

join this group.

http://www.mini-lathe.com/

been a member for a long time.

 

[onthefence777]

mini-lathe.com is actually one of the resources I heavily studied when I first got into this, never noticed the premium content section! Thanks for pointing that out! Unfortunately I don't have funds to sign up right now, but look forward to when I do.

For anyone else that might come across this, I am convinced that I do need to turn the spacer down by maybe a couple of mils. as it is, the gear that directly drives the headstock is offset of the rest of the geartrain. Also, at higher speed with no pressure applied, after about 20 seconds it slowly decreases in speed as the load increases from it beginning to heat up.

I think this is not a mini lathe exclusive question, so if anyone has any comments they are appreciated.

 

[PugetDude]

Heat=Expansion. What you describe the headstock play in the starting condition should actually be the running condition.

 

[onthefence777]

Agreed.

Ran it some more at moderate speeds idle for a while, then a few finish facing ops, a few rough facing ops, held up fine. Couple of high speed finish ops, then high speed idle, and it slowed down quick. For about 30 secs the chuck was super tight, then loosened back up.

Going to take that spacer down a tad tomorrow and see what I get.

 

[royesses]

Go to and sign up, the best friendliest hobby forum there is :
http://www.hobby-machinist.com/
You don't need to cut down the rear spacer for the angular contact bearings. They are exactly the same size as the original deep groove bearings. You need to shorten the rear spacer approx. .100" for the tapered roller bearing upgrade to keep the gears aligned. I've done both to my 7x10. Both upgrades require setting up preload on the bearings. This is done with the two spanner nuts on the end of the spindle.

The way to check the preload is to run in the bearings while monitoring the bearing temperature looking for a approximate 20° to 25° temperature rise. Thick grease will cause high temperature rise as will too much preload. Typically you tighten the spanner nut until there is no end play as measured with a dial indicator and then tighten the spanner about 1/16 turn more. Lock down the spanner lock nut and then check end play and then bearing temperature by measuring the headstock above the bearing.

It is very doubtful you harmed the motor with too much preload. The brushes wear out from a lot of use.

Check the alignment of the spindle gear to forward/reverse gears to see if you need to change the spacer.

Roy

 

[onthefence777]

Go to and sign up, the best friendliest hobby forum there is :
http://www.hobby-machinist.com/
You don't need to cut down the rear spacer for the angular contact bearings. They are exactly the same size as the original deep groove bearings. You need to shorten the rear spacer approx. .100" for the tapered roller bearing upgrade to keep the gears aligned. I've done both to my 7x10. Both upgrades require setting up preload on the bearings. This is done with the two spanner nuts on the end of the spindle.

The way to check the preload is to run in the bearings while monitoring the bearing temperature looking for a approximate 20° to 25° temperature rise. Thick grease will cause high temperature rise as will too much preload. Typically you tighten the spanner nut until there is no end play as measured with a dial indicator and then tighten the spanner about 1/16 turn more. Lock down the spanner lock nut and then check end play and then bearing temperature by measuring the headstock above the bearing.

It is very doubtful you harmed the motor with too much preload. The brushes wear out from a lot of use.

Check the alignment of the spindle gear to forward/reverse gears to see if you need to change the spacer.

Roy

Thank you! That is immensely helpful!

So I should aim for that gear on the spindle to line up centered on the gear it is driven by? Thats awesome, I can just measure the difference and cut to size.

I never read about that process before. Can you elaborate just a little more? Mainly, about "end play". I'm not quite sure what you mean there. What do I need to measure with the dial indicator?

I used a blue mobil grease on the advice of my neighbor who helped me swap out the bearings, like a wheel bearing grease. Made sense to me since the angular contact bearings are pretty much like the wheel bearings on a car just a bit smaller.

Fortunately, I do have a laser thermometer and a dial indicator, so I can follow your process if you can explain that one point. I knew someone here could help!

 

[royesses]

On the rear of the spindle are 2 spanner nuts pressing against the drive gear. That gear mates with the forward and reverse gears mounted on a pivoted yoke with a spring loaded lever in the back of the head stock. This allows running the lead screw in both directions. Those two gears must mate with the spindle gear and they need to be in line with the spindle gear as close as possible. The spacer is what will control this. If the spacer is too short the spindle gear will be to the right of the other gears and will not have full mesh.

Actually the spindle gear drives those two gears which in turn drive the change gears. The motor drives the counter shaft through a belt and the counter shaft drives the spindle through the high/low gears.

If angular contact bearings are installed you had to press them onto the spindle and also press them into the housing. They look just like the original bearings and may or may not be sealed.

Tapered bearings look just like the front wheel bearings on a car. They are separate inner and outer races that have tapered rollers on the inner race.

If tapered bearings are installed you pressed the front inner bearing on the spindle and the outer bearing race(cup) into the head stock. The rear outer race also known as the cup is pressed into the rear of the headstock and the rear inner bearing is a sliding fit on the spindle for ease of adjusting preload.

End play is how far forward and back the spindle can move when pushed in and out. You want 0" end play so the spindle can not move in and out while you are cutting metal. I place a magnetic indicator base on the top of the head stock and set the indicator plunger against the face of the spindle. Then pry the spindle to the right and left to get the end play measurement. if there is any end play the spindle spanner nut must be tightened to remove the end play. Then the nut needs to tightened a tiny bit more to squeeze the bearings together causing preload. This a a "feel" type thing. Next tighten the second spanner nut to lock the first and re check end play to make sure you have not upset the preload. With the high/low gear lever in neutral so no gears in the headstock are meshing you should feel a small drag on the spindle when you turn it but this also is effected by the thickness of bearing grease. So perfection would be a relatively free turning spindle with no end play. End play will result in tool chatter and sometimes strange patterns on the material getting machined.
It is difficult to get perfection! You do the best you can.

The blue Mobil grease should be ok for this. The recommended grease is Mobil 1 synthetic SHC-32 spindle grease. There is no need to go to this until you again have to grease the bearings which could be years.

Note the temperature measurements will be measured at the highest speed and could slightly exceed the suggested range. Lets say 140° is about as high as I would go. The grease gets hot due to a shearing action and can raise the temperature quite a bit.

There are two forums on the hobby-machinist site for the HF mini lathe. There are tons of information and many pro's to answer questions.

I have purchased way too much from Little machine shop. They are great people and carry everything you could possibly want for a mini machine.

Roy

 

[onthefence777]

I did sign up on that forum last night and started cruising it, just waiting for approval. Awesome website!

Thanks for elaborating. I apparently was using the wrong word, I in fact did install tapered bearings.

I will be digging into this later today to make adjustments, thanks for the in-depth details sir!

 

[royesses]

I did sign up on that forum last night and started cruising it, just waiting for approval. Awesome website!

Thanks for elaborating. I apparently was using the wrong word, I in fact did install tapered bearings.

I will be digging into this later today to make adjustments, thanks for the in-depth details sir!

My pleasure. You will get any help you need on that forum. Enjoy the lathe and feel free to ask questions on the hobby machinist forum. No flaming or arguments or ploitics allowed. Just great people helping each other.

Roy