Excessive runout with threading jig

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FGarbrecht

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Long story short -- I tried making a threading jig and it wasn't accurate enough to suit me (excessive runout), and so I bought a Chefwarekits threading jig. I know this is marketed primarily for threading larger wooden objects but I thought that with a small threadmill I could adapt it for pen threading. I measured the runout of the jig (measured along circumference of my ER32 collet holder) at 0.017" which is too much for threading tiny objects like pens. I tried threading a section just to give it a try and the runout caused one side of the section wall to blow out. I have an email in to them to see if they have any suggestions but thought I'd try the experts here to see if anyone has used this jig for pen threading and what you may have had to do to tune it up. Thanks.
 
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bmachin

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Fred,

Don't own one of these, but just from looking at it I suspect you're barking up the wrong tree.

1. Just don't think the fixture, especially in combination with the way it is attached to the lathe, is anywhere rigid enough to do the kind of threading that you want it to do; i.e. any kind of pen thread.

2. If you're looking to do cap/ barrel threads, you're going to need a mill with a really small nose radius (~.002).

Just out of curiosity, why do you want to do this? If I'm not mistaken, you have a metal lathe. If so, why not just single point your pen threads?

My uninformed $0.02

Bill
 

FGarbrecht

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Fred,

Don't own one of these, but just from looking at it I suspect you're barking up the wrong tree.

1. Just don't think the fixture, especially in combination with the way it is attached to the lathe, is anywhere rigid enough to do the kind of threading that you want it to do; i.e. any kind of pen thread.

2. If you're looking to do cap/ barrel threads, you're going to need a mill with a really small nose radius (~.002).

Just out of curiosity, why do you want to do this? If I'm not mistaken, you have a metal lathe. If so, why not just single point your pen threads?

My uninformed $0.02

Bill
I suspect you're correct that this may not be the right machine for the job. I'm looking for a way to cut threads in wood though and my understanding is that the metal lathe method for thread cutting would make a mess of it. I confess that I haven't tried. Everything I've read suggests that metal lathe threading as well as tap/die cutting don't work well on wood.
 

Curly

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Bruce came up with a way to do them and insured another to make a variation. Maybe there is something in them that might help.


When you measure your collet chuck where exactly are you putting the indicator tip? Regular dial indicator or a finger type?
 

FGarbrecht

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Bruce came up with a way to do them and insured another to make a variation. Maybe there is something in them that might help.


When you measure your collet chuck where exactly are you putting the indicator tip? Regular dial indicator or a finger type?
I put the tip of the dial indicator midway between the end of the collet chuck (collet end) and where it seats onto the threaded portion of the jig (I made sure the collet chuck is seated very firmly on the jig), and I made sure the tip of the indicator was at right angles to the longitudinal axis of the chuck. I have a common dial indicator with the little plunger at the end (not sure what a finger type is).

I'll check out those links, it looks like I'm going to have another go at building my own. At some point during construction of the first (and failed) home made jig, the costs were mounting up so I decided to go commercial. My mistake I guess.

thanks
 

bmachin

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. . . the metal lathe method for thread cutting would make a mess of it. I confess that I haven't tried. Everything I've read suggests that metal lathe threading as well as tap/die cutting don't work well on wood.
Believe that you're absolutely right here. I think that I tried it once on african blackwood and it was an utter failure.

I am willing to eat some words after looking at the links that Pete posted. Guess I missed them the first time around. Note though, that both of those builds are much more substantial than the Chefware.

I'll take a mulligan in that I was thinking more along the lines of triple start 33 or 36 tpi. :rolleyes::rolleyes:

In addition to those Pierre has done quite a few wood pens which he has shown both here and at FPN. As I recall he used a "V" form thread although I might be mistaken.

Bill
 

Curly

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The indicator is more commonly called a test indicator. The finger like tip lets you get into the inside of bores and narrow spaces. Range of measurement is 0.030" or less in 0.0005" or 0.0001" increments.

I reread your first post and using the outside of the chuck may give you erroneous readings. Better is to take a collet out and put the tip of the indicator on the inside taper the collets seat on.
 

FGarbrecht

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Believe that you're absolutely right here. I think that I tried it once on african blackwood and it was an utter failure.

I am willing to eat some words after looking at the links that Pete posted. Guess I missed them the first time around. Note though, that both of those builds are much more substantial than the Chefware.

I'll take a mulligan in that I was thinking more along the lines of triple start 33 or 36 tpi. :rolleyes::rolleyes:

In addition to those Pierre has done quite a few wood pens which he has shown both here and at FPN. As I recall he used a "V" form thread although I might be mistaken.

Bill
Yes, I’m copying Pierre’s work😯. He uses a router based jig and a single point cutter that he made. He has shared some of his threading secrets but I’m too lazy and/or unskilled to make it work (yet).
 

FGarbrecht

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I may have solved my problem. Looking at my homebuilt jig, the runout is coming from slop in the attachment of the spindle adapter to the threaded rod. Putting a bunch of teflon tape on the end of the spindle adapter to fill the slop / gap brought the runout down to 0.003" which may be good enough. I haven't looked at the commercial jig yet but I suspect the same issue. Common threaded rod is just too sloppy for precision work. I haven't been able to find anything called 'precision' threaded rod, so I may have to finally learn how to do my own metal lathe threading.
 
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