Size??

[jttheclockman]

On a PSI #2 mortise pen mandrel, what is the actual size of the rod and the thread size?? Looking to get some extra rod and nuts for future projects. Do not want to buy mandrels. Need a few of them so if i can get rod I can cut my own size lengths. Thanks. I am guess all #2 mandrels are of equal dimensions. ???

 

[monophoto]

John -

To answer the specific question, I measured the mandrel rod as 6.2mm, with a 1mm pitch thread. Probably would be a good idea for someone else to make the measurements, and then compare. You know - the measure twice rule.

But it seems to me that the important thing is to know the ID of a pen tube. If the tube fits over the mandrel, you can choose whatever threading and nut you want to use - there's no need for your extra nuts to be interchangeable with the knurled nut supplied by PSI. The tube in the one kit I grabbed at random measured about 6.05mm ID.

And before someone else chimes in - in this case, size does matter.

 

[jttheclockman]

Boy I have to say I have been away from pen turning too long. I had one of those brain meltdowns and I am going to blame it on older age syndrome. That is my story and I am sticking to it. So simple use 1/4" rod and nuts. Sometimes you just out think yourself. What a dingbat. Thanks anyone who tried figuring out what I wanted. Man I need to get back in the shop.Much safer there.

 

[Edgar]

I think 1/4" will work fine if you cut threads and use nuts, but I don't think it will fit into a mandrel saver, so it might not work for those who want to use mandrel savers. DAMHIKT

 

[MPVic]

Boy I have to say I have been away from pen turning too long. I had one of those brain meltdowns and I am going to blame it on older age syndrome. That is my story and I am sticking to it. So simple use 1/4" rod and nuts. Sometimes you just out think yourself. What a dingbat. Thanks anyone who tried figuring out what I wanted. Man I need to get back in the shop.Much safer there.

Thanks John, you make me feel so good - good to know I'm not the only one!!

 

[jttheclockman]

Thanks John, you make me feel so good - good to know I'm not the only one!!

I think these moments are coming way too often though. The 1/4" threaded rod will work just great for what I have in mind. Trying to keep mind busy so when I do hit the shop again I can have the thinking part done.

 

[egnald]

Greetings from Nebraska! I don't know for sure about the PSI mandrel or it's threads, but I use a Water Hard, D Drill Rod (0.246 inches diameter +/- 0.0005 inches) from Granger. The fit is snug (sometimes very snug depending on the tolerance of the bushing IDs, but the C (0.242 inches) seemed a little too loose and 1/4 inch was far too tight. A light touch with a round file on the inside of any bushings seems to address any tight fits on the D size nicely. A 3-foot piece runs less than $6.00. Regards, Dave (egnald).

 

[monophoto]

I was thinking about Edgar point about mandrel savers, and that triggered me to review this thread this morning, and when I reread my post from Tuesday, my measurements didn't make sense. Then I realized that I had made the measurements downstairs in the shop, and then tried to remember them long enough to walk back upstairs to the office to do the post. Obviously, that was a dumb thing to do! So I repeated the process, being careful to first zero out the caliper, and then write down the measurements rather than try to remember them.

So - for the record, the correct measurements are:

PSI mandrel rod OD - 6.17mm​

7mm tube ID - 6.27mm.​

iEngineer tells me that 1/4" is equivalent to 6.35mm. I don't have a mandrel saver, but my understanding is that they are simply a hollow live center that the mandrel slips through so that the tail stock pressure can be applied to the bushings on the mandrel rather than to the mandrel itself. On that basis, Edgar's comment makes sense. But it also suggests that a tube supplied with a standard 7mm pen kit won't fit over a rod that is exactly 1/4" in diameter.

Another example of why we need to abandon the imperial measurement system!

 

[jttheclockman]

I was thinking about Edgar point about mandrel savers, and that triggered me to review this thread this morning, and when I reread my post from Tuesday, my measurements didn't make sense. Then I realized that I had made the measurements downstairs in the shop, and then tried to remember them long enough to walk back upstairs to the office to do the post. Obviously, that was a dumb thing to do! So I repeated the process, being careful to first zero out the caliper, and then write down the measurements rather than try to remember them.

So - for the record, the correct measurements are:

PSI mandrel rod OD - 6.17mm​

7mm tube ID - 6.27mm.​

iEngineer tells me that 1/4" is equivalent to 6.35mm. I don't have a mandrel saver, but my understanding is that they are simply a hollow live center that the mandrel slips through so that the tail stock pressure can be applied to the bushings on the mandrel rather than to the mandrel itself. On that basis, Edgar's comment makes sense. But it also suggests that a tube supplied with a standard 7mm pen kit won't fit over a rod that is exactly 1/4" in diameter.

Another example of why we need to abandon the imperial measurement system!

I get what you are saying and all that makes sense. With that said I probably should have asked what size rod fits into bushings and left out the mandrel part. I want to be able to set up blanks on a rod with the bushings to have an idea how thick I can build the blank without it being exposed when turned down. Thus the need for the rod to sit on my jig that will hold it as I build the blanks. Right now when I do this I just doublesided some tape to a dowel and built the blank and guess the thickness. The tube sits on the dowel but with so many different size tubes I figured this would work better. With the bushings right there no more guess work.