# which pen mandrel threads



## Geo in Winnipeg (Aug 17, 2007)

I've noticed there are two threads - 1/4x20 tpi and 1/4x28 tpi used for pen mandrels. I know one is coarse and the other is fine thread but is one better than the other? Or is it just personal preference.


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## Randy_ (Aug 18, 2007)

George:  If that is correct, I would say it doesn't make a whole bunch of difference one way or the other in terms of use.  It is my impression that the more common threading is 1/4-28 and I don't recall ever seeing 1/4-20 used??

Woodcraft makes a mandel that has a 10/24 thread and will "ONLY" fit their arbors so be careful if you buy from them.


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## jcollazo (Aug 19, 2007)

I sell the 1/4-28 threads 5:1 over the 1/4-20 threads. It really is just a matter of preference. Maybe there's a particular thumbnut or wingnut someone likes to use .... who knows. My mandrels now come with the nylon thumbnuts w/ hexnut insert so users can now mix and match.


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## scubaman (Aug 19, 2007)

Because the 1/4-28 thread is finer, it applies more pressure for the same torque.  I think Berea is the only company using 1/4-20.  Berea makes mandrels for others also.

In practical use it does not make a whole lot of difference.  I only finger-tighten mandrel nuts.  I have standardized on 1/4-28 on the mandrels I make simply because the finer thread is a little easier to cut in drill rod.  But I've used Berea mandrels for years before that.


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## Randy_ (Aug 19, 2007)

> _Originally posted by scubaman_<br />.....I think Berea is the only company using 1/4-20.....



Just to clarify what Rich said, the Berea Precision mandrels are threaded on both ends with the 1/4x28 thread and use the ubiquitous knurled brass thumb nut.  IIRC, their High Precision Drill Driver mandrel is only threaded on the tailstock end and uses an ordinary 1/4x20 hex nut.  

I have seriously considered sicking Frank on these guys as it doesn't make much sense to me why they use different threadings on the different mandrels??


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## toolcrazy (Aug 19, 2007)

Well, we have another entrant in the field. I'm not sure what thread it is, but my PSI pro mandrel isn't 1/4 28. It's slightly smaller than that. When I ordered Joe's replacement rods I ordered the 1/4 28, and the PSI brass nut won't fit Joe's replacement. It's no biggie, I just use the one supplied with the new rod.


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## Randy_ (Aug 20, 2007)

> _Originally posted by toolcrazy_
> <br />.....I'm not sure what thread it is, but my <b>PSI pro mandrel</b> isn't 1/4 28.....



I don't see such a mandrel mentioned in the PSI catalog.  Are you possibly talking about their adjustable mandrel that they call the Maxi-Mandrel??


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## Rifleman1776 (Aug 20, 2007)

> _Originally posted by Randy__
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   I'm here. [}][]


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## Geo in Winnipeg (Aug 20, 2007)

Thanks for all the replies. I kinda thought the only reason was pretty much personal preference. I couldn't see any glaring reason why one would be that much better than the other.


> _Originally posted by Randy__
> 
> I have seriously considered sicking Frank on these guys as it doesn't make much sense to me why they use different threadings on the different mandrels??


Maybe they're trying to make their mandrels "proprietary". The few mandrels I have are 1/4-28 so I think I'll stick with that.


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## Randy_ (Aug 20, 2007)

George/Steve:  You guys got my curiosity fired up.....and that is usually bad news for someone.  I have fired off an email to PSI to see if I can find out what kind of threading they are using on their pen mandrels.


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## jcollazo (Aug 20, 2007)

> _Originally posted by toolcrazy_
> <br />Well, we have another entrant in the field. I'm not sure what thread it is, but my PSI pro mandrel isn't 1/4 28. It's slightly smaller than that. When I ordered Joe's replacement rods I ordered the 1/4 28, and the PSI brass nut won't fit Joe's replacement. It's no biggie, I just use the one supplied with the new rod.



That could be the ultra fine 1/4-32. I personally have not seen any of those.


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## loglugger (Aug 20, 2007)

I have mandrels with 3 different threads 1/4 20, 1/4 28 and a 1/4 finner one, don't know where it came from.
Bob


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## toolcrazy (Aug 20, 2007)

> _Originally posted by Randy__
> <br />
> 
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Yes, Randy, it's their adjustable mandrel. I think I got it mixed up with another brand, oh well. [] It came with my starter kits, oh so long ago. It is a nice tool, with the exception of the crappy rod. But I fixed that, thanks to Joe.


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## jcollazo (Aug 20, 2007)

> _Originally posted by loglugger_
> <br />I have mandrels with 3 different threads 1/4 20, 1/4 28 and a 1/4 finner one, don't know where it came from.
> Bob



Scan that puppy and post the pic. Something else I've never seen![]


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## Randy_ (Aug 20, 2007)

> _Originally posted by jcollazo_
> <br />
> 
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I commented earlier about the Woodcraft mandrel that had a 10/24 thread on the headstock end.  I have no idea what the thread is on the tailstock end but I'm guessing it is 1/4-28 since it uses those brass knurled thumb nuts.  Anyway, maybe my memory was faulty and the Woodcraft mandrel might actually have a 10/32 thread instead.  

I've already sent off an email to PSI.  Guess I will send one to Woodcraft as well.  Maybe not.  I just looked at their catalog and their technical service people are open until 9 P.M.  kinda weird since customer service is only open till 5 P.M. ??  I'm hanging on hold right now so we will see what happens??


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## loglugger (Aug 20, 2007)

I will get to the shop tomorrow and get a reading on it. I know that the nut ot it will not fit the 20 or 28.
Bob


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## Randy_ (Aug 20, 2007)

> _Originally posted by toolcrazy_<br />Well, we have another entrant in the field. I'm not sure what thread it is, but my PSI pro mandrel isn't 1/4 28. It's slightly smaller than that. When I ordered Joe's replacement rods I ordered the 1/4 28, and the PSI brass nut won't fit Joe's replacement. It's no biggie, I just use the one supplied with the new rod.



Why did I think things were going to be simple.....should have known better!!  PSI just responded to my email and now we have something new in the mix.  They tell me that the thread on their Maxi-Mandrel is 6mm.  They neglected to quote the pitch or maybe they were telling me something?  According to the references I have, there are 3 standard pitches for a 6mm thread: 1, 0.75, and 0.5.  Using standard convention, they would be annotated as follows: M6, M6 x 0.75, and M6 x 0.5.  The first is the coarse thread, has a pitch of i, and by convention, the pitch designation is dropped. The second two are the fine and extra-fine threadings.  For those of you who are not familiar with the metric convention, the pitch of a thread is essentially the length of one fill thread in mms.  A pitch of 1 means that there is exactly 1mm between identical points on any two adjoining threads.  Converted to UNC terminology, it is the equivalent of about 25-1/2 threads per inch.  A pitch of 0.75 is the UNF equivalent of about 34 tpi and a pitch of 0.5 is the UNXF equivalent of about 51 tpi.  If Steve is so inclined he can count the threads on his original PSI mandrel and let us know what he finds.  Since the PSI guys said only that it was a 6mm thread, it is quite possible they were saying it is the metric coarse thread with a pitch of 1 or tpi of 25Â±.

Does that get everyone up to speed or just confuse you further??[][]


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## Randy_ (Aug 20, 2007)

> _Originally posted by loglugger_
> <br />I will get to the shop tomorrow and get a reading on it. I know that the nut ot it will not fit the 20 or 28.  Bob



Bob:  Be prepared to find that it is a metric thread.  If it is a 6mm thread, the major thread diameter will be about 0.236".


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## loglugger (Aug 21, 2007)

Shalf is .244 threads .228 some where between the 20 and 28 thread closer to the 20. This is one I never used very mutch because the bushings fit to loose on the shalt, A metric nut will fit but don't know the number, I am trying to ignore the whole metric thing, just to old to learn the whole thing all over.
Bob


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## Randy_ (Aug 21, 2007)

Hey Bob:  The 0.244" shaft diameter sounds like it might be a PSI mandrel.  Their catalog says their mandrels are 0.243".  CSUSA and Berea mandrels are 0.245 to 0.247".  And now a question for you.  Is the 0.228 measurement correct.....maybe a typo??  I looked at the chart I have for threads...both American and metric and there is no standard threading for that dimension and nothing even close nothing close??  I wonder if you misread your vernier?  Maybe you could double check that measurement for us?  Thanks


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## tas2181 (Aug 21, 2007)

My original maxi-mandrel measures .244' and the major thread diameter measures .232" or 5.88 mm. Thread count is ~26/28 per inch. I have been using the mandrels from Joe lately.


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## Randy_ (Aug 21, 2007)

> _Originally posted by tas2181_
> <br />My original maxi-mandrel measures .244' and the major thread diameter measures .232" or 5.88 mm. Thread count is ~26/28 per inch. I have been using the mandrels from Joe lately.



That appears to be a less than perfect M6 thread which would be 0.236" on the major diameter and 25.4 threads per inch.


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## rixstix (Aug 21, 2007)

My M6 1.0mm die screws onto the PSI mandrel with no problem.  My M6 1.0mm tap will not screw into the nut.


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## Randy_ (Aug 21, 2007)

I spent some time on the phone with one of the Woodcraft technicians today and he was very helpful.  Pulled some parts off the shelves and measured them up for me.  The tailstock end of both their basic Morse taper mandrel and their Pro mandrel(adjustable) had a 1/4x28 thread.  The headstock end of the basic mandrel has a 10-32 thread.  My earlier comment calling it a 10-24 thread was in error.  There is, of course, no thread on the headstock end of the Pro mandrel.


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## loglugger (Aug 21, 2007)

merometer .244 shalf  .228 threads  with a mitutoyo digital calipers it is shalf 6.17 mm threads 5.80 mm. The bolt that I took the nut off of is also threads 5.80 mm. Thats my story and I am sticking to it. []
Bob


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## Glass Scratcher (Aug 22, 2007)

> _Originally posted by Randy__
> <br />I spent some time on the phone with one of the Woodcraft technicians today and he was very helpful.  Pulled some parts off the shelves and measured them up for me.  The tailstock end of both their basic Morse taper mandrel and their Pro mandrel(adjustable) had a 1/4x28 thread.  The headstock end of the basic mandrel has a 10-32 thread.  My earlier comment calling it a 10-24 thread was in error.  There is, of course, no thread on the headstock end of the Pro mandrel.



Glad you posted this.  I just ordered some Thumbnuts from Jay, with the fine nuts.

I discovered the gnurled brass nut on my Woodcraft mandrels are not drilled/tapped square and I have a feeling that the uneven tension from the nut may have been causing some out of roundness.  But of course it could just be all me.


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## Randy_ (Aug 22, 2007)

> _Originally posted by rixstix_
> <br />My M6 1.0mm die screws onto the PSI mandrel with no problem.  My M6 1.0mm tap will not screw into the nut.



That's a real puzzle.  Can't even begin to speculate what is going on therer??


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## Randy_ (Aug 22, 2007)

> _Originally posted by loglugger_
> <br />I have mandrels with 3 different threads 1/4 20, 1/4 28 and a 1/4 finner one, <b>don't know where it came from.</b>



Hey Bob:  Every time I have your thread figured out, you fire in a curve ball that messes up my thinking again!!  Can you even guess as to where that mandrel might have come from??  Do you recall ever buying from PSI or one of their resellers?  Do you recall the vendors that you have purchased from so we can figure out where that mandrel "MIGHT" have come from??




> _Originally posted by loglugger_
> <br /> I will get to the shop tomorrow and get a reading on it. I know that <b>the nut ot it will not fit the 20 or 28.</b>



Can you make a careful thread count of the mandrel thread?  I know it is hard to do on those finer threads, especially if you have eyes like mine; but getting an accurate thread count would be a big step in identifying the thread.




> _Originally posted by loglugger_
> <br />Shalf is .244 threads .228 some where between the 20 and 28 thread closer to the 20. This is one <b>I never used very mutch because the bushings fit to loose on the shalt</b>, <b>A metric nut will fit but don't know the number,</b> I am trying to ignore the whole metric thing, just to old to learn the whole thing all over.



The PSI mandrel has a publuished shaft diameter of 0.243 which is the smallest of all of the mandrels that I know of.  As a result, many of the bushings from other manufacturers tend to be a little loose on the PSI mandrels.  Might mean something or may just be coincidence??

The closest metric threading to the figures you have posted is an M6.  That threading should have a major diameter of 0.236" and 25.4 threads per inch.




> _Originally posted by loglugger_
> <br />merometer .244 shalf .228 threads with a mitutoyo digital calipers it is shalf 6.17 mm threads 5.80 mm. The bolt that I took the nut off of is also threads 5.80 mm. Thats my story and I am sticking to it.



Your micrometer and your caliper are getting the same readings.  I still feel like it is an M6 thread.  Since the thread on the bolt seems to be the same as the one on the mandrel, it doesn't seem like we are looking at a worn thread or a special proprietary thread.  I sure would like to know what you have there; but we may not be able to figure it out with the resources that are available to us.


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## Randy_ (Aug 22, 2007)

For those who are interested, here is the source of my thread size data.  there is a wealth of technical data here on all sorts of subjects.  Scroll down to the "T"s for the threading charts.

http://mdmetric.com/techindex.htm


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## loglugger (Aug 22, 2007)

Randy, If you realy want to know PM me your adress and I will send it to you as I will not be using it.
Bob


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## Randy_ (Aug 22, 2007)

Thanks for the offer, Bob; but I don't think it is really worth it to go to that trouble.


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