Is there a prize for the worst thread ever cut HELP!

[pippin88]

Shouldn't imperial threads be cut with a 55° tool? (Not that this affects your cut quality)

[Pete F]

Shouldn't imperial threads be cut with a 55° tool? (Not that this affects your cut quality)

No, he is cutting UNF not Whitworth.

[th62]

The cut with the tangential was a one off for a comparison only. Most cuts were done at .02mm on the compound. That is the smallest cut I can make (aside from moving the compound half a graduation). And of course with the compound set at 28 degrees, the cut would be less than .02mm. I'll try half graduation cuts today anyway.

The 58 degrees I mentioned was a typo, the compound is set at 28 degrees. With the compound at that angle, if you rest the cutting edge of the tool against the side of the compound slide, the tool sits parallel with the top slide (one or two degrees off). But I'll try moving the compound to 28 today and also try plunging.

I doubt very much if it's the spindle bearings as it's a new machine, but I will reset all gibs and check spindle bearing pre load just to rule them out as a problem.

The material is standard bright I bought from Greens not too long ago and it machines nicely with HSS, just not threading apparently.

After two solid days I'm starting to run out of patience.

Pete F, I read your tips on a previous post and also on another forum - very helpful. I'm assuming the Pete F on the other forum is you!

Thanks also to the rest of you, your tips will give me something to do today, if I don't kick the lathe to death first...

[Pete F]

Pete F, I read your tips on a previous post and also on another forum - very helpful. I'm assuming the Pete F on the other forum is you!

I think some people consider one Pete F on the internet is more than enough.

It's a shame I'm not still in Adelaide, as I was there last week and could have swung by to drink all your beer and dispense copious quantities of pointless statements of the obvious until the beer ran out. Sadly you'll have to settle with me taking another look at your pictures now I'm at a larger monitor and see if there's anything obvious I can see.

[Pete F]

Ok yes, I think there's something funky going on with your tool grind there in picture #4, however it's quite a small picture. Can you post a larger picture of your tool you've ground please?

[simonl]

Generally, if I get unsatisfactory results when cutting, I straight away look to the tool geometry. I find 90% of the time it's because I have failed to create sufficient clearance for the cutting edge or a similar issue. It's rarely a DOC or feed rate problem because I tend to err on being very conservative with such. I'm not doing it for a living so I see no need to unnecessarily load up the machine. Also, it's always 100% my fault no matter where the problem lies, so no use in kicking the machine even though I feel the same way sometimes!

If you can't produce a 0.02mm DOC without chatter then something is definitely wrong. Are you sure they didn't give you some spring steel or something?

Simon

[th62]

Kicking inanimate objects always makes me feel better I've noticed - with the possible exception of the big toe of course.

It is never my fault, not when there is a shed full of tools to blame - fortunately I'm not a tradesman.

Luckily I didn't have to resort to kicking though, it appears the problem was the apron clamp/guide.

This morning I checked the spindle preload, then tore apart the compound and top slides, cleaned up, reassembled and adjusted gibs. But when I grabbed the apron and shook, I found a little movement at the front.. The carriage guide/clamp appears to have been the problem, so I shaved a smidgen off and did the same to the rear guide/clamp, and reassembled. Runs smoothly along the bed with no knocking when changing direction now.

Ground another bit (no honing and no helix), clamped in holder with a 12mm overhang and (with fingers crossed) cut a thread using coolant and the compound, finishing of with a couple of very fine plunge cuts to smooth the trailing edge of thread. Huge improvement, the thread isn’t cut to correct size or cleaned up after - just a roughy to test straight off the tool. Still not as good as I’d like, but approaching useable. Presumably attention to tool sharpening should improve. I may send off for a diamond or Arkansas stone next and try that.

I did cut another with a reshaped tangential/diamond bit with much the same results.

The picture of the thread was shot from a distance of around 25 - 40mm and brushed off with a rag for clarity. Sorry about the quality but the camera won't focus unless I shine a torch on the object.

I noticed from new when winding the carriage back and forth there was a bit of a knock when changing direction, probably the apron moving up and down. Should have checked that when first setting the lathe up.

[Pete F]

It's very difficult to tell from your photos, but I wonder if you have sufficient end relief on the tool? Associated with that is ensuring the tool is exactly on centre when threading. If the end relief isn't sufficient or the tool is above centre it will rub and will likely cause issues such as you've described.

[KBs PensNmore]

th62 where did you buy the lathe from, hope it wasn't ozmestore on fleabay? Unless it's from a reputable firm, a lot of lathes are thrown together. I've read that some places suggest that the lathe be stripped down completely, washed of rust preventative, lubricated and assembled/adjusted correctly. Axminster in the UK sell units that are ready for use or ones that you do yourself. I know the one I was given, had done about 4 hours work, had to have the apron dismantled and adjusted the same as what you did, with some judicial filling to be done in certain places. Diamond files can be bought from Bunnies.
Kryn

[Pete F]

I've just grabbed a couple of my V thread tools, one is 55 degrees and one is 60 degrees, but it really doesn't matter for this purpose. This is what your tool should look like. Obviously the one on the left in the first photo is upside down, but I wanted to get both tools in the same photo.

Threading tools side.jpg

Threading tools top.jpg

[Techo1]

It's very difficult to tell from your photos, but I wonder if you have sufficient end relief on the tool? Associated with that is ensuring the tool is exactly on centre when threading. If the end relief isn't sufficient or the tool is above centre it will rub and will likely cause issues such as you've described.

The end relief has nothing to do with the tool rubbing, the tool appears OK in that respect, extra side clearance to allow for the helix angle of the thread is what is required to stop the tool rubbing on the leading edge.

[Jekyll and Hyde]

This morning I checked the spindle preload, then tore apart the compound and top slides, cleaned up, reassembled and adjusted gibs. But when I grabbed the apron and shook, I found a little movement at the front.. The carriage guide/clamp appears to have been the problem, so I shaved a smidgen off and did the same to the rear guide/clamp, and reassembled. Runs smoothly along the bed with no knocking when changing direction now.

Glad to hear you seem to have sorted it. When I was looking at the photo of your earlier attempts before I read on to the end, I was thinking it looked like there were varying depths in the thread, as though something was flexing or moving under load and then springing back. Wasn't sure if it was just the photo though, but though I'd throw that comment in now anyway on the off chance it's not just the photo, and someone else has the same issue at some point...

[Pete F]

The end relief has nothing to do with the tool rubbing ...

Ok, what do you think the end relief is there for?

[simonl]

I inherited my lathe when it was less than 12 months old. After deciding to change the oil I noticed sand and all sorts of other stuff draining out with the oil. So with that I decided to strip it down and clean. Unfortunately it was all to late for the spindle bearings as they were shot.

Just because you have a new Chinese lathe, doesnt mean its in top condition!

Simon

[Grahame Collins]

I am please to see you have found the cause of your troubles.

A good mate, a mechanic ,from my younger days often used to say
" Always look for the simple things first" It is truly amazing how often he was right.

I admit to doing almost the same thing as you in having the gib strip loose on the cross slide.

Also I tried the cut with a bit of unknown steel and it was coarse and tore instead of cutting.

It was a good thread to remind people just like me to check on these sorts of things.To me information like this is priceless bit of trouble shooting and gets stored in my computer under a lathe file for quick reference when I next forget something basic.

Thanks to th62 and each and every one of you who have contributed.

Grahame