[aarongough]

Hey all!
I've finally setup my mini lathe, and have spent the last few days getting to know it... Unfortunately I've noticed one major issue:

Whenever I take a cut, the depth of cut varies slightly (maybe a couple of thou) depending on the handwheel position. So I end up with a slight wave pattern on the work that corresponds with the handwheel position. It seems like the carriage is rocking slightly when I am applying pressure to turn the handwheel.

I have already adjusted the carriage strips to the point where any tighter and the carriage will bind in place.

I'm thinking this might be related to lack of a proper oil film on the ways (I don't seem to be able to oil it so that the carriage leaves an oil film in it's wake, it seems to scrape the ways clean of oil instead).

I also seem to be unable to get any sort of decent surface finish when turning the OD of a part. Facing cuts are beautiful and clean, but as soon as I move to the OD I get a scraped, gummy looking appearance marked with bands.

It might be worth mentioning that the ways on this lathe are somewhat crappy. I checked them with the edge of a good 6" square and there was light showing through all over the place. The dips didn't seem to correspond with any marks on the work though.

Any advice will be well received!

[MichaelHenry]

Where did you get it and is it still "new"? Sounds like the ways are very bad and you might be better off exchanging it for one in better shape.

What sort of material are you cutting? 6061-T6 aluminum usually turns pretty well, but the type of aluminum found at hardware stores can be gummy and difficult to turn with a nice finish. 12L14 steel also turns well. I'd start with something like those that is easy to turn to give you some confidence and eliminate other factors that could be causing you problems.

Make sure you use the right feed and speed for the material and cutter.

Present the cutter at the correct angle to the work.

Use a cutter that is ground properly for the material you are turning. Sherline sells pre-ground tools and you might want to consider those to get started.

Mike

[aarongough]

Where did you get it and is it still "new"? Sounds like the ways are very bad and you might be better off exchanging it for one in better shape.

What sort of material are you cutting? 6061-T6 aluminum usually turns pretty well, but the type of aluminum found at hardware stores can be gummy and difficult to turn with a nice finish. 12L14 steel also turns well. I'd start with something like those that is easy to turn to give you some confidence and eliminate other factors that could be causing you problems.

Make sure you use the right feed and speed for the material and cutter.

Present the cutter at the correct angle to the work.

Use a cutter that is ground properly for the material you are turning. Sherline sells pre-ground tools and you might want to consider those to get started.

Mike

Hey Mike, thanks for the response!

I've had the machine for many months and am only now getting the chance to use it, so no returning it unfortunately.

I actually was trying to turn both 6061 and 12L14, both of them came out with pretty rough finishes...

This morning I decided to take the plunge and pull the lathe apart. As it stood it was pretty much useless, so there wasn't much to lose.

I drilled 3 extra holes through the saddle so I can inject oil in underneath it. I then spent an hour sorting out the saddle gibs (which are crazy tricky...).

The force required to move the saddle is waaay less now that I'm able get oil in the right places. It seems like adjusting the gibs made a lot of difference too, previously they were bearing only on the edges of the ways rather than being flat.

After all this was done the lathe is at least cutting straight lines rather than shallow sine wave patterns like it was before. The surface finish on parts is better, but still pretty terrible.

I'm using insert tooling from LMS mounted in a Tormach 0XA QCTP. The tools are these one: Turning Tools, 3/8" Indexable TCMT Inserts - LittleMachineShop.com

I have tried both HSS and carbide inserts, both seem to give roughly the same finish. I am aligning the tools on center by taking facing cuts until the little nub goes away, so I'm relatively sure I'm turning right on center.

I could live with the surface finish as it is, but it's bad enough to stop me from doing any real precision work. I tried to turn a sleeve and shaft to a hydraulic fit earlier today and found I couldn't get the same fit the length of the part (which was only about 1"). The lathe is really only a beginner step into turning for me, I know that I'll move onto a better lathe at some point, but it would be nice to get whatever potential I can from this one first, as I'm sure I'll learn a lot in the process...

[691175002]

Generic inserts are almost always awful.

I picked up a kit from tools tooling for hobby lathes (they also have 3/8") and the aluminium inserts are absolutely beautiful. There has got to be like a 40 degree rake on them.

HSS tooling should do a very good job as long as you grind them properly. High positive rake and very sharp.

[aarongough]

Ok, I'll have a look into other inserts and see if that makes any difference.

Here is a photos of a spring center I made today as an example of the surface finish. The main barrel of the center has a lot of uneven 'ring' type markings. Some of them may well be due to my less than expert control of feed rate, but in other places where I was able to maintain a constant speed I definitely still noticed similar blemishes. The barrel was treated with some emery cloth, so the blemishes that remain are the worst of them, there were plenty more before the sanding.

[aarongough]

Generic inserts are almost always awful.

I picked up a kit from tools tooling for hobby lathes (they also have 3/8") and the aluminium inserts are absolutely beautiful. There has got to be like a 40 degree rake on them.

HSS tooling should do a very good job as long as you grind them properly. High positive rake and very sharp.

So to be clear: if I want to buy inserts for my current tooling then I would be looking for 3/8" TCMT or TCMW inserts, is that correct?

Are there any sites that better explain what the codes for the inserts mean?

EDIT: Accidentally managed to answer my own question: http://www.carbidedepot.com/formulas-insert-d.htm

[691175002]

The picture does not look like an insert problem, although finishing the piece with emery paper pretty much makes it impossible to judge surface finish.

[aarongough]

The picture does not look like an insert problem, although finishing the piece with emery paper pretty much makes it impossible to judge surface finish.

I wouldn't be surprised if it was all down to uneven feed. No matter what I do I can't seem to get that front handwheel turning evenly, and having the cross-slide handwheel in the way does not help.

Unfortunately when I first got the lathe I was intending to CNC it pretty quickly so I took apart the threading/power-feed system. I then proceeded to lose many parts of the power-feed, not an ideal situation.

[Vogavt]

No matter what I do I can't seem to get that front handwheel turning evenly, and having the cross-slide handwheel in the way does not help.

It looks like your cross-slide might be racking up and digging in sporadically.

Why aren't you letting the machine make the traveling move for you?

That's what the lead screw on the front )that you're manually turning the front hand whee on) is supposed to do. It's not "just" for turning threads.

Factory settings for the Gears are A=20, B=80, C=20 & D=80.

Calculates out to be 256tpi, which is pretty fine if you're taking light cuts.
You must be quick on the draw to get it to stop at the right place.

[aarongough]

It looks like your cross-slide might be racking up and digging in sporadically.

Why aren't you letting the machine make the traveling move for you?

That's what the lead screw on the front )that you're manually turning the front hand whee on) is supposed to do. It's not "just" for turning threads.

Factory settings for the Gears are A=20, B=80, C=20 & D=80.

Calculates out to be 256tpi, which is pretty fine if you're taking light cuts.
You must be quick on the draw to get it to stop at the right place.

Unfortunately I lost some parts of my power feed assembly, otherwise I would definitely be using it...

[hoss2006]

Unfortunately I lost some parts of my power feed assembly, otherwise I would definitely be using it...

LMS has tons of spare parts.
Replacement Parts: 7x10/12/14 Mini Lathe (C2/C3) - LittleMachineShop.com
Hoss

[aarongough]

Here's an example of the surface finish on 12L14:



I have noticed that sometimes the carriage will jam a little, I think swarf may be getting trapped sometimes under the edge of the carriage.

[aarongough]

Here is the best surface finish I've managed to get so far:



Here is the setup I used:



Took the cut at about 2200 RPM, with a very slow feed and only about 0.001" DOC

I honestly have no idea if this is considered a 'good' surface finish (I assume not) so input would be great.

[Nine8Six]

Just got the SIEG SC2 7X12 lathe and I am getting near/same finishes as yours mate. Not as bad tho lolll Brand new lathe, properly alinged and adjusted (well, as far I can help it) but the backlash on both the Z&X is awful not mentioning the rocking effect of the lead screw locking thing!

Just got myself proper ballscrews and coupler kit to CNC it with nema23 motor, drivers etc. The only way to get a 'near' pro finish on one of those 7x12 I'm pretty sure. $800 kit extra on top of the lathe itself so really hope that will sort the issue of poor finishes and uneven, or, ramdom cuts.

Luck on your side