Question about mini-lathe setup (maybe)

[Mike6158]

I have a Little Machine Shop Hytorque 7x16 mini-lathe (Part number 5100). I've had it for a while but haven't done much with it. A few days ago I decided to try to remake some pulley's and spindle for the pulleys. The diameter of each pulley was 0.500", hole and corresponding spindle diameter is 0.090" x 0.500", and the other end of the spindle had a 0.250" hex with 6-32 UNC threads after the hex. While turning the v-grove in the pulley's and sometimes when turning the hex stock down (two different tools), I would move the tool in with the compound and it would stop cutting. I kept moving the tool in and nothing happened. Then it would "jump" and turn quite a bit (relatively speaking) off of the part. At least once it ruined the part by turning it down too far. The parts are pretty small so it was hard to tell how much force was being put on the stock.

I checked compound movement and it wasn't binding up. It seemed like the tool was binding or maybe set too low and was lifting the stock or maybe the stock was riding up on the tool? I'm not sure. I was cutting brass. I was using insert tooling, I believe it was carbide. Yes- I will be reading the thread on grinding my own HSS tooling.

I know this is fairly vague but I'm hoping that I made a common mistake and someone here will recognize it. In the end I made my parts but

 

[Jubil]

It takes more pressure to make an insert cut, some inserts more than others. Be sure cutter is sharp. You may be taking a depth of cut that is too much for the your lathe.
You are cutting a small diameter (.500"). Stay as close to chuck as possible, 1-1/2 times diameter of work. Make sure gibs are adjusted properly. Set tool height to center.
If I stall the work I always back out instead of increasing pressure. Allow work to start turning then ease back in.
I'm just repeating things that I've seem on this forum. I'm sure someone else will come along who knows more than I and give you some real help.

Chuck

 

[MarkDavis]

My second hand harbor freight lathe did the same, always wondered if the tool finally got a bite on the stock.

So was it the slop in the lathe? or the quality of the cutting edge?

Still have not figured it out, the harbor freight lathe sits on a shelf across the garage (nice coating of dust). The two year old Precision Matthews lathe gets all the attention now.

Joined this forum, and my cutting tools are getting better too.

 

[mikey]

Mike, I'm going to guess that your tool was set above center height. When that happens your cutting edge is riding too high and the part just below it is contacting the work. Intermittently, it will dip down as you apply infeed pressure and the tip will dig in, cutting excessively all of a sudden.

Lathe tools need to be at center height. There are many ways to get it there but a height gauge made to the exact centerline of your spindle is the best. Many designs out there - one of the easiest to make is the Hardinge L-2A.

 

[RobertB]

Make sure gibs are adjusted properly. Set tool height to center.

Lathe tools need to be at center height.

^^Both very important! ^^

No slop in the gibs, tool centered. Watch some of the youtube videos on setting tool height. Make a test facing cut, if you are left with a little nub on the end of the piece, your tool is not centered.

 

[owl]

Also, if you are turning to .090, you must limit stick out to avoid flex in your workpiece, make light cuts with a very sharp tool. It may be possible to put on a follower rest to hold the workpiece more rigidly.

 

[Ken from ontario]

I own a LMS 5200, the compound slide must be locked prior to cutting. although there's no factory built locks on these lathes but due to it's lack of rigidity, your lathe will benefit greatly if you added a lock on the two main moving parts, the cross slide and compound slide.
If you have already done these modifications and still have that problem when cutting, I'm afraid I don't have an answer for you but will follow this thread to find out what the cause is ,I've never had to deal with this sudden jump of the cross slide .

 

[homebrewed]

I have turned brass with carbide inserts with no problems. I was using my 7x12 mini lathe with no compound or cross slide lock.

Since brass is a "grabby" metal, it can self-feed if your lathe has some slop in it. In particular, if the cross slide feedscrew nut isn't properly adjusted it can have a lot of play in it. In this scenario, you wind the cross slide in until it engages the brass, which then pulls the slide in until the backlash is removed. This jumpy action repeats each time you advance the cross slide.

This is just one possibility. As noted in other replies, the cutter has to be on center, and your cross slide/compound gibs should be adjusted for minimal play.

FYI, the ideal cutter for brass shouldn't have much, if any, positive rake because brass can grab. The worst instances of this I've seen is when enlarging holes in brass by step-drilling. So grinding your own HSS tool for brass is a good idea, too.

 

[ptsmith]

I own a LMS 5200, the compound slide must be locked prior to cutting...

I locked my mini lathe compound with the gib adjustment screws. It made a huge difference.

 

[Mike6158]

Wow, why didn't I post to this forum sooner? I'd be so much farther along. I corrected my post... I typed cross slide when I meant compound. I'm going to try to combine responses and replies.

Center - yes. I have an Edge Technology tool centering widget. What can I say, I like widgets. BUT, the tools were put into new tool holders (is it possible to have enough tool holders? I think not) and I can't remember if I had centered them when I faced off the stock or I was just winging it. Probably the latter. I also have a 1/2" diameter tool that looks like the Hardinge tool. I got it from Joe Pieczynski but don't have it with me (I live in 2 places, not because I'm wealthy or want to... work is in one place, home is in another, for now)

Sharp tool - The insert tooling was brand new. It came from Amazon. I seemed to cut pretty well. Here's what I used:

Adjusting gibs... I've read the LMS document a few times and I can't say that they made a lot of sense to me. I don't know how much tension they should have on them. My cross slide and compound are pretty easy to spin. Not sloppy easy but not a lot of resistance. Backlash is a whole different issue. I know the compound has too much backlash, 0.005" by the dial. The cross slide has 0.0025" by the dial. I think homebrewed touched on this one and I can see how it would happen

I have a compound lock and I use it unless I'm roughing, threading (haven't tried that yet, etc).

I'm one of those people that studies something to death and then dives in... I've studied lathes for over 3 years (not by using though) and I've had mine for a little over a year. I've watched and watch Clickspring make magic, Abom79 make huge stuff, Tom Lipton at OxTools sloppy work (.00000001 tolerance... really Tom... can't you tighten it up just a little ), This Old Tony... more magic, James at Clough42, and Joe Pieczynski for a couple of years now. There's more than that but between grandkids, aviation, electronics, ham radio, machining (learning to anyway), photography, work, and whatever I'm forgetting I don't have enough time to watch or do what I'd like to. Good problem to have

Here's my setup for grooving the shaft for a c-clip. A very, very small c-clip. I put the 1/2" stock in a collet, center drilled it, drilled and tapped it for 6-32, and that is how I plan to hold the spindle.