Author Topic: Turned my first pen....  (Read 21122 times)

Offline Bernd

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Re: Turned my first pen....
« Reply #25 on: April 22, 2009, 09:24:30 PM »
Tough choice you gave me there. :med:

Bernd
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Offline websterz

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Re: Turned my first pen....
« Reply #26 on: April 23, 2009, 01:09:32 PM »
Tough choice you gave me there. :med:

Bernd

At least he didn't ask what your sac looks like. :jaw:
"In the 60's, people took acid to make the world weird.  Now the world is weird and people take Prozac to make it normal."
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Offline Divided he ad

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Re: Turned my first pen....
« Reply #27 on: April 23, 2009, 05:21:27 PM »
Quote
At least he didn't ask what your sac looks like.  :jaw:

Hold on a mo'..... I didn't even get a picture so you can't laugh at me too much!!!  :lol:



I'm definitly going to have to put pen research onto my never ending list!  :coffee: 




Ralph.
I know what I know and need to know more!!!

Offline Bernd

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Re: Turned my first pen....
« Reply #28 on: April 23, 2009, 05:52:08 PM »
Chris,

E-mail resent. Did you get it?

Bernd
You can't fix "STUPID".

Offline raynerd

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Re: Turned my first pen....
« Reply #29 on: April 24, 2009, 01:53:54 AM »
Bernd - yea pm sent back.

Offline Darren

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Re: Turned my first pen....
« Reply #30 on: April 24, 2009, 07:59:15 AM »
This was on another forum, I don't claim to understand it, just passing it on.

When using the threading dial, there are three things that come into the equations -- thread pitch, or TPI (as set by the gearing), leadscrew TPI and teeth on the thread dial. There's no one size fits all... you need to calculate if it's not all in the book.

For example, on my 618 I often do 4 lead 36 TPI threads, so I set the gearing to 9 TPI, use a 16 tooth thread dial with a 16 TPI leadscrew so each quarter mark on the dial is a different thread start.

But once I tried to do a different setup that was impossible with the thread dial. I think it was 32 TPI four or three lead.

Using a bit of trig you can always set up for multiple starts in any setup. If you can do one thread start with the thread dial, you can do other thread starts by simply resetting the 0 positions of the compound and cross slide by moving the compound by twice the pitch and moving the cross slide by square root of three times the pitch. Just move them in opposite directions. Then use the thread dial the same way as the previous start. It's really not that hard once you've done it.
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Offline John Hill

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Re: Turned my first pen....
« Reply #31 on: April 24, 2009, 07:08:38 PM »
Darren, I would have to read that a few more times before I could claim competance!


What would be the chance, especially for soft material, to make a multi point tool?  For example, the 36TPI 4 start thread, start with a short length of 36TPI male thread which you braze at right angles across the end of a square steel bar then grind down the round threaded bit until you have a multi point tool.  Set the feed to 9TPI and presto! 36TPI 4 start thread! :med:

You could also use a bit of a 36TPI tap or a broken die nut.

BTW, were not the earliest threads cut with such multi pointed tools?  Is that not the form of the original 'thread chaser'?  Maybe such things are still available? :scratch:

[Bogs probably has a set of them!]

[Still thinking, maybe a fragment of 36TPI hacksaw blade? :coffee:]
« Last Edit: April 24, 2009, 07:15:34 PM by John Hill »
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Offline John Hill

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Re: Turned my first pen....
« Reply #32 on: April 24, 2009, 07:12:26 PM »
OK, here is a thread chaser, for wood though.

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Offline sbwhart

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Re: Turned my first pen....
« Reply #33 on: April 24, 2009, 07:15:31 PM »
That is spot on John  :thumbup:

That is what I was on about using a chaser for I probably didn't explain it well   :scratch:

Cheers

Stew
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Offline Darren

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Re: Turned my first pen....
« Reply #34 on: April 24, 2009, 07:17:54 PM »
I get the gist of it John, he's saying cut 4x 9tpi threads using the dial indicator to give the correct positioning for each start.

Ending up with a 36tpi thread with four starts...if I understand it correctly. It doesn't sound that hard to do?

But then I haven't tried it  :lol:
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Offline raynerd

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Re: Turned my first pen....
« Reply #35 on: April 25, 2009, 04:50:07 PM »
Just to clarify something with multiple start feeds, take this scenario:

Two pens are ready to thread the barrel for the barrel/cap thread - one is threaded 36TPI quad lead and the other is threaded 9TPI standard single lead. When I come to screw the cap on the pens, in my mind the cap will go up the thread the same distance per turn (revolution) on both pens, however the quad lead will catch the start of the thread quicker - right? A pen maker I spoke to said that a multi lead thread allows the cap to be turned up the pen further (i.e tightened or released quicker) with less revolutions of the cap. This to me makes no sense as they are both 9TPI but with the quad lead, you just have 4 of them running parallel. Clearly there is something I am not getting. Do the threads on a multi lead thread cross?

The pen maker also said a multi lead thread is "stronger" but I don`t know what he means by that.

Thanks for the posts so far, really informative.

Chris






 

Offline John Hill

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Re: Turned my first pen....
« Reply #36 on: April 25, 2009, 04:52:44 PM »
That is spot on John  :thumbup:

That is what I was on about using a chaser for I probably didn't explain it well   :scratch:

Cheers

Stew

UM, sorry Stew, :bow:  I didnt read your posts carefully enough to realise you were talking about the thing I had in mind.
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Offline sbwhart

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Re: Turned my first pen....
« Reply #37 on: April 25, 2009, 05:23:41 PM »
No worries John  I was just pleased someone else was on the same wave length as me.

Stew
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bogstandard

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Re: Turned my first pen....
« Reply #38 on: April 25, 2009, 05:35:22 PM »
Just to put your minds at rest, here is a little info for you to chew over, it might put things straight.

What you are making is a 9tpi thread multiplied by four but at the same depth as a 36 tpi one, all running parallel to each other. So the multistart will travel forwards four times faster than a single cut 36 tpi thread.

This pic explains it a lot better than trying to tell you, it is based on a standard four lead screwthread. See how far forwards it moves for each revolution.



It is for that reason, chasers shown above cannot be used for cutting multistart threads. They will only cut or dress a single thread.

Darren, it can be an absolute pig to do.

The main problem, the smaller the TPI, the faster the cut over a given length is done. Also, this lathe is designed for a min TPI of 12, by making it do 9TPI would grossly overload the gear train when driven by the spindle, and so has a tendency to smash the gears or holding bolts (I have had it happen to me), so you have to modify the lathe so that the drive comes from the leadscrew, usually by fitting a handle onto the end of the leadscrew and turning it by hand. This solves two problems, the first being the stress on the gear train, and the second being, you don't have to have the reactions of a s**thouse rat to to disengage the half nuts before the cutter hits the chuck when doing it under power.

These are columns I made for one of my engines, they are based on a 2.5 TPI, two start thread, using a specially ground cutting tool. Doing these on my large lathe under power, smashed the heads off two 3/8" diameter gear train holding bolts like they were lollipop sticks. So it does happen, if anyone doesn't believe what I am telling them. They are only just over 1/4" diameter, so it wasn't the cutting itself that caused the breakage, it was the stress in the geartrain trying to move the saddle across at high speed to do the cutting.





Bogs
« Last Edit: April 25, 2009, 11:51:43 PM by bogstandard »

Offline raynerd

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Re: Turned my first pen....
« Reply #39 on: April 25, 2009, 09:12:14 PM »
Cheers Bogs - understood. As always, your post is incredibly informative and I now both have a better understanding of multi-lead threads and the capabilities of my lathe. As you have already told me, I am going to have to modify my lathe so that the gears can be cut my hand to reduce stress on the gear train and this shouldn`t be a problem because any threads I cut with low TPI will be on soft materials anyway and will be perfectly OK cutting by hand turning.

bogstandard

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Re: Turned my first pen....
« Reply #40 on: April 25, 2009, 11:45:50 PM »
Chris,

The material won't come into the equation. Because you will be using such a large gearing advantage, you will most probably be turning a few times on the handle to get 1 turn on the chuck, so you could put any material you liked into the chuck, and if you have the right material for the cutter in the toolholder, it will cut it.

The handle should be demountable, so that when used as a normal lathe, it won't be hitting you in fragile places.

John

Offline raynerd

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Re: Turned my first pen....
« Reply #41 on: April 26, 2009, 03:30:23 AM »
OK, look forward to our visit and you can explain more in person.

Chris