Novice Lathe Questions

[Hood]

Yes, a threading tool holder will hold the insert at the correct angle, it will also likely have a shim to give the correct helix angle.
A TCMT holder probably won't hold a threading insert securely and definitely wont be at the correct angle.

 

[mylesdw]

Thanks for that, so more expense...

In that case my efforts went surprisingly well but I did break a tip or two.

 

[Seadog]

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)

Try cutting the thread away from a shoulder. It can be done very quickly.

 

[Hood]

Same - carbide tools really need a fairly high surface speed to get a good finish, when threading that's a recipe for disaster!....

Ideally they do but that does not mean it needs to be. Friday I was turning a prop shaft for a boat. 316 1.5" dia x 3m long with a 1:12 taper and a 1" BSF thread. I could not spin this fast due to the unsupported length through the spindle bore, there was probably 2m sticking out the back of the lathe. I threaded at probably 150rpm, maybe less and it was nice. It is quite a common occurrence for me to do that rpm on similar threading jobs.

 

[mylesdw]

I fitted a quick change toolpost to the lathe. China's finest but seems to do the job, time will tell. The toolpost and one holder cost less than $150 whereas the machining needed to fit it was $300!

The holders seem ridiculously cheap at $19 each.

 

[mylesdw]

Has anyone been through the whole process of having a lathe bed reground? It seems to me that getting everything to fit and align afterwards would be a massive task. How would you re-align the lead-screws?

 

[Richard.]

@Pete. has just had his done on his beautiful machines
He’ll be able to tell you what it’s like to rebuild it.

 

[Pete.]

Has anyone been through the whole process of having a lathe bed reground? It seems to me that getting everything to fit and align afterwards would be a massive task. How would you re-align the lead-screws?

You're right in that if you grind the bed and/or the underside of the saddle it will move the apron down in relation to the leadscrew. On my HLV I machined some thickness off the underside of the saddle and glued some low-friction way liner to it, then machined and scraped it to fit. This lifted the saddle up to it's original height. I actually used the leadscrew to get the height right by removing the support bearing from it's housing and measuring the gap above and below using gauge blocks.

On my Southbend the grinding guy took the same amount off the underside of the apron where the saddle bolts up as he did off the ways. This lifted the apron the same amount as the ways dropped and allowed the leadscrew to line up properly. An unfortunate side-effect of this is that it also closed up the centre distance between the cross-slide screw gear and it's driving gear in the apron. I am going to have to re-cut the gear on the new cross-slide screw I made about 10 thou smaller to get that clearance back.

Other methods that can be used are to make a clay dam on the bedway, apply a release oil and block up the saddle to it's proper height then pour in moglice so that it fills the gap. I've seen it done in photos but never tried that myself. Looks messy but I guess it must work or they wouldn't do it.