And now: a swing-up tool for internal threads

[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 As long as the tool is withdrawn on the last cut all the previous rubs will be removed anyway.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) with a single point tool  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

Best Regards

picclock

[Pete.]

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

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.

[Ned Ludd]

Hi Andy,
The Cox one is not the only one of these internal tools, see 
 http://www.model-engineer.co.uk/forums/postings.asp?th=53342#1013705   
for details.
Ned

[andyf]

Hi Ned,

Yes, indeed - Chris Stephens and Mike seem to have been working independently on the same idea. Chris posted his first on the ME forum, about a week before Mike:
http://www.model-engineer.co.uk/forums/postings.asp?th=52176&p=3
And John Bogs was designing one, too. Maybe he will have further improvements to suggest in the fullness of time.

The swing-up toolholder, particularly for external threads, seems such a simple concept, and performance reports from those who have made one all seem favourable. Hence, it's surprising that either no-one invented the thing until recently, or that is is an old idea which has been forgotten until Mike re-invented it.

Andy

[Ned Ludd]

Hi Andy,
Could well be a case of great minds think alike. Rather like the telephone, two people invented in the same week.

The external swing up holder mechanism is not new, it is in effect the working parts of a shaper, what is new is its use for threading, for which Messrs Cox and Moore deserve the credit. Coxy for the idea and Bogs for bringing it to fruition and making it known to a wider audience. Seems odd that now we have to differentiate between internal and external holders, life was so much simpler when there was only the one.
Ned