Novice Lathe Questions

[Pete.]

Just about any engineering adhesive. I'd go for a 2-part oil resistant epoxy.

 

[mylesdw]

Failed miserably with 5-minute epoxy and the proper engineering stuff really expensive for the amount I needed but...

success with super glue and the gib works well. The play in the carriage had gone and the trial cut looked much better.

Problem is, the movement of the carriage is now limited. To the right there is plenty of travel; I seldom turn anything long but it was nice to be able to 'park' the carriage all the way to the left up against the headstock while doing drilling/tapping/reaming operations. Guess I'll just have to live with that?

 

[MattF]

So the carriage gets tight/stuck when you move close to the headstock? Sounds like you need to adjust the gib for full length travel. You usually have tight and loose spots due to bed wear, so it's a case of finding the centre point between the two. If you can't get it up there by adjusting the gib, you've shimmed it too much.

 

[mylesdw]

Still getting very rough results. This is 3/8" diameter mild steel at around x25 zoom. The surface is varied and rough. Carbide tool (TCMT) and 700rpm between chuck and live centre. Around the slowest feed rate and that final cut about 0.012" With/without oil seems to make very little difference, sometimes oil appears to make it worse.

 

[squazy84]

sometimes regular mild steel can be such poor quality over here it tares rather then cuts,try a different piece of material just to be sure?

 

[MattF]

As Squazy' says, there's some lousy stuff to machine out there. Better getting a piece of something you know can be machined, and trying that.

 

[mylesdw]

That's better! Tried a different piece of steel. The first one came from the scrap bin at the steel supplier so I don't know what it is. This one I bought as bright mild and although not perfect I'm much happier with that. I didn't realise the steel would make such a difference.

 

[Seadog]

I used a piece of 1" blackstock that's been kicking around the workshop for 20 years to make up something recently. I had the devil's own job to get a decent finish on it. In fact, despite trying HSS and carbide, with and without lube and at different cutting speeds, I couldn't get a decent finish. It looked more like a giant bar code, as you can see in the photo. I managed to polish most of the banding out, by hand with emery and oil, and ended up with a finish that was fine for the job in hand.

 

[whm_fab]

ive had the very same problem with unknown steel too. i got some steel bar from a friend that strips and scraps industrial printers, i thought i had won the lottery with all the free steel (which looked lovey) it machined exactly like your top photo, no matter what i did. ended up weighing the lot in

 

[mylesdw]

Threading inserts question

I've done a little external threading using a carbide threading insert and the results have been acceptable, although I discovered that it is very easy to break the tips off.

The tips I bought, you simple choose internal/external and the angle, 60° in my case.

I see now that there are tips available for pretty much every thread pitch too; you can get a 16 tpi insert and a 12 tpi insert and so on. Is there any great advantage in using these rather than the the 'general' 60° ones I have?

 

[Hood]

The ones for each pitch/TPI are full form so they will cut the correct root and crest for the thread in question.
Is it worth it for someone just messing about or doing odd jobs? Probably not as likely you do not need your threads to have the perfect root and crest.

 

[Pete.]

You can do it but you have to bear in mind that ISO threads are specified with a tip flat that is Pitch/4 for an outside thread. A 1mm pitch insert would have a tip width of 0.25mm, a 2mm insert would have 0.5mm and so on. With the correct tip width you should be able to stop when it starts showing in the run-out groove and the nut should fit. So the answer is if you're going to use a single insert, use a finer pitch one with a narrow flat then you can over-cut the depth a little for coarser pitches but you'll have to keep test-fitting the nut if you want a close fit.

https://en.wikipedia.org/wiki/File:ISO_and_UTS_Thread_Dimensions.svg

Also if you think you're at or past the full depth but the nut still won't fit, check the OD hasn't increased. It's easy to raise a burr on the OD when thread cutting which will make you think that you've messed up your calcs/measurements/setup when all that's happening is the nut is binding on the burr. If you find the OD has grown just run a file over (carefully) it with the lathe turning, and check the OD until it's back down where it should be.

 

[Hood]

..... So the answer is if you're going to use a single insert, use a finer pitch one with a narrow flat then you can over-cut the depth a little for coarser pitches but you'll have to keep test-fitting the nut if you want a close fit.....

I think he is meaning that he uses the partial profile inserts, if so then these inserts still have a range that they can cut, often it is 0.5 to 3mm pitch.

 

[Richard.]

I religiously thread with hss tools. I made a set of 55° and 60° when I first bought the lathe and I’ve never had to touch them since. I cut with carbide as I prefer the finish but thread with hss. I just take it easy with threads, slow speed and a small progression on the top slide every cut.

 

[Hopefuldave]

I religiously thread with hss tools. I made a set of 55° and 60° when I first bought the lathe and I’ve never had to touch them since. I cut with carbide as I prefer the finish but thread with hss. I just take it easy with threads, slow speed and a small progression on the top slide every cut.

Same - carbide tools really need a fairly high surface speed to get a good finish, when threading that's a recipe for disaster!
My lathe stops on the proverbial sixpence since it has both mechanical and VFD braking, there's a quick-withdraw on the cross-slide for threading, but trying to cut coarse threads at 600+ rpm really doesn't leave much time to react, particularly if one's an old duffer like me...

Dave H. (the other one)

 

[Richard.]

but trying to cut coarse threads at 600+ rpm

Ha I wouldn’t even attempt that on mine. I pluck away at the slowest speed of 48 rpm when cutting a thread. Nice and easy. No rush.

 

[Hopefuldave]

I don't attempt it - but it's the sort of speed that carbide wants! I thread as fast as I can cope with, as even HSS likes about 40 fpm and that works out at 640 rpm or so on a 1/4" thread... Which I would probably thread at 200 or so, then thwack the clutch lever as I got near the end, dropping it to about 40!

I've used a Hardinge a few times, they happily thread at 600 RPM and have a very handy single-tooth clutch in the leadscrew drive that disengages at an adjustable stop, like some of the other Holbrook and other toolroom lathes, makes threading a relaxed and pleasant experience

I must make something similar for mine, given the Tuits, I've got the CAD models for various parts done...

In the meantime, I've a Coventry die head, another easy-threading option (but the dies are a fortune).

Dave H. (the other one)

 

[Pete.]

I don't attempt it - but it's the sort of speed that carbide wants! I thread as fast as I can cope with, as even HSS likes about 40 fpm and that works out at 640 rpm or so on a 1/4" thread... Which I would probably thread at 200 or so, then thwack the clutch lever as I got near the end, dropping it to about 40!

I've used a Hardinge a few times, they happily thread at 600 RPM and have a very handy single-tooth clutch in the leadscrew drive that disengages at an adjustable stop, like some of the other Holbrook and other toolroom lathes, makes threading a relaxed and pleasant experience

I must make something similar for mine, given the Tuits, I've got the CAD models for various parts done...

In the meantime, I've a Coventry die head, another easy-threading option (but the dies are a fortune).

Dave H. (the other one)

I'll do you a demo of threading at 1000rpm when I get my Hardinge rebuilt. Been looking forward to it

 

[Windy Miller]

I'll do you a demo of threading at 1000rpm when I get my Hardinge rebuilt. Been looking forward to it

Give me a shout when it's done Pete - I'd love to see that in the flesh!

 

[mylesdw]

Threading inserts question

I've done a little external threading using a carbide threading insert and the results have been acceptable, although I discovered that it is very easy to break the tips off.

The tips I bought, you simple choose internal/external and the angle, 60° in my case.

I see now that there are tips available for pretty much every thread pitch too; you can get a 16 tpi insert and a 12 tpi insert and so on. Is there any great advantage in using these rather than the the 'general' 60° ones I have?

I've just noticed that the suppliers sell special holders for the threading inserts. I've just been using them in the turning/facing tools that I have (TCMT). Is there something special about a threading tool rather than a turning/facing tool (holder)?

https://www.rdgtools.co.uk/acatalog...e-Tool--60-degree---16-tip--1623.html#SID=550