Mother of Pearl Blanks

[studioseven]

Yesterday I turned my first mother-of-pearl blank. It was a challenge because the material was very fragile and tended to chip easily. I worked slow, took small passes and was able to finish turning and sanding the blank. Then disaster struck when I went to assemble the pen. A small crack appeared on the inside of the blank (not on the exterior). The farther I pushed the transmission in, the longer the crack grew. I had used a chamfering tool prior to assembly on both ends of the blank. Anyone have any suggestions on what else I may try to prevent this in the future? Appreciate your advice.

Seven

 

[magpens]

Ream out the brass tube so that it slides onto the hardware fairly easily and glue.

I use straight-sided adjustable reamers for this ... available from Grizzly and/or HF.

 

[brownsfn2]

Where did you get the blank? Do you have pictures?

 

[studioseven]

The blank was a mother-of-pearl from PSI. It was a 7mm size. I will try and get a picture of it.

Seven

 

[brownsfn2]

Oh I see. I have seen those blanks. Those are the mass produced ones. They do tend to be a bit more brittle due to the process they follow. It was the same with the old circuit board blanks they sold. Mass produced PR blanks like that just tend to not turn as well.

 

[Kenny Durrant]

Mal I have this trouble from time to time as well. I looked up reamers at Grizzly and saw they have a set of adjustable ones. Is that what your using or do you have a one size does it all? Thanks

 

[studioseven]

I also looked up the reamers. The smallest I could find is a 1/4". Will that fit inside a 7mm tube?

Seven

 

[Curly]

I also looked up the reamers. The smallest I could find is a 1/4". Will that fit inside a 7mm tube?

Seven

A quick search would tell you the answer is yes. 7mm = 0.2756" and 1/4" = 0.250".

 

[studioseven]

7mm is the outside diameter. What is the inside diameter?

 

[Curly]

Whoops. Walls are generally about 0.014 thick so that would make the inside of the tube close to 0.245". So it might not fit. I did find a number of 6.0 to 6.5mm adjustable reamers on Ebay for about $10.00Can/$8.00US that should do the trick if the 1/4" was too big to start. Or you could get the 6.5mm-7mm if you didn't want the imperial set. Or a metric set though aliexpress.

https://www.ebay.ca/sch/i.html?_fro...ers.TRS0&_nkw=6mm+adjustable+reamers&_sacat=0

https://www.ebay.ca/sch/i.html?_odk...S0&_nkw=6.5+-+7mm+adjustable+reamers&_sacat=0

https://www.aliexpress.com/item/The...rch0104.8.43.495cc61abHkhWh&priceBeautifyAB=0

https://www.aliexpress.com/item/9pc...rch0104.8.56.495cc61abHkhWh&priceBeautifyAB=0

 

[ed4copies]

7mm is the outside diameter. What is the inside diameter?

7mm is the diameter of the HOLE they tell you to drill. The tube fits inside the hole--so we really don't have any clue what the diameter is. One of my pet peeves in this industry--totally inaccurate "specs"!!!

Measuring with a caliper that is only so-so on INSIDE diameters, I get .244", far from 7mm, which is .27559055"
But it does confirm that you quarter inch reamer won't fit IF it is really .25"!!!
I use a chainsaw file to solve your original problem.