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And now: a swing-up tool for internal threads

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andyf:
Many will recall the swing-up toolholder for external threads devised by Mike and developed further by John (Bogstandard) as shown here: http://madmodder.net/index.php?topic=2323.0

Mike now has a working prototype for cutting internal threads, which can be viewed on his website: http://mikesworkshop.weebly.com/prototype-internal-swing-up-toolholder.html 

As will be seen, he is thinking of combining the two swing-up holders (for internal and external threads) into a single double-ended unit.

Andy

picclock:
I'm sure this has been discussed before (probably suffering from brainfade), but what is the downside of just reversing the lathe without the toolholder swinging up ?

I'm sure its theoretically a bad thing but I've done threads this way without apparent issue - I've even cut threads without using the compound by just forcing the tool in and doing repeated cuts, [hangs head in shame]  (cos the compound was removed and I thought it would work and it did), although the thread finish was not as good as with using the compound.

So the tool gets rubbed backward by the work on the return - probably pushing the carriage as the leadscrew backlash will make it ineffective. The carriage (at least on my lathe) moves fairly easily, the work is soft, the tooling hard. As long as the tool is withdrawn on the last cut all the previous rubs will be removed anyway.

I'm not saying its desirable, but for cutting a few threads in a non production environment to me it seems a bit unnecessary unless the threads are so small and fine that the carriage load would cause issues.

If I've missed something please let me know what it is. Not looking to start a war here just trying to find out if the benefits are real or illusory.

All comments - especially the ones explaining my erroneous assumption - welcome.

Best Regards

picclock

DaveH:
picclock,

Mainly the backlash in all the gears that cause the problems. Tends not to line up so good in the thread.

Another point (gee I'm good) :D with a single point tool  :D of the insert type like I tend to use - it chips the point because it does not like being rubbed the wrong way.

DaveH

picclock:
Hi Dave

With inserts it makes much more sense - I tend to use HSS for stuff like that cos it seems to give a better finish. It also helps for the first cut or two to 'bias' the carriage wheel toward the tailstock until a groove is established. Obviously works best for coarse threads (pitch > backlash).

Just happen to be doing some M10 threads today so I thought I'd throw in my bad practices for free :wave:

Best Regards

picclock

Pete.:

--- Quote from: picclock on July 15, 2011, 04:24:38 AM ---I'm sure this has been discussed before (probably suffering from brainfade), but what is the downside of just reversing the lathe without the toolholder swinging up ?

I'm sure its theoretically a bad thing but I've done threads this way without apparent issue - I've even cut threads without using the compound by just forcing the tool in and doing repeated cuts, [hangs head in shame]  (cos the compound was removed and I thought it would work and it did), although the thread finish was not as good as with using the compound.

So the tool gets rubbed backward by the work on the return - probably pushing the carriage as the leadscrew backlash will make it ineffective. The carriage (at least on my lathe) moves fairly easily, the work is soft, the tooling hard. As long as the tool is withdrawn on the last cut all the previous rubs will be removed anyway.

I'm not saying its desirable, but for cutting a few threads in a non production environment to me it seems a bit unnecessary unless the threads are so small and fine that the carriage load would cause issues.

If I've missed something please let me know what it is. Not looking to start a war here just trying to find out if the benefits are real or illusory.

All comments - especially the ones explaining my erroneous assumption - welcome.

Best Regards

picclock

--- End quote ---

Do you actually do this on your own lathe. On the occasions where I have reversed my lathe without withdrawing the tool it has always chewed the thread up quite nicely. I can't imagine that the first cuts of a thread are deep enough to drive the carriage backwards on many, if any, lathes.

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