Machinable Ceramics and Threads

[drawoh]

Has anybody had experience with screw threads in machinable ceramics like Macor. My actual problem is that workers are pulling thread inserts (Keen-serts) out of G10 FR4 backing plates. I am looking for an electrical insulator that retains screw threads.

--
JHG

 

[rothers]

The tapped holes need to be blind ?

 

[drawoh]

rothers,

No.

--
JHG

 

[rothers]

Can you fit a headed insert from the back ?

Plenty to choose from but one example: Link

 

[EdStainless]

Some people claim to machine all sorts of features into Macor, but I have had no such luck.
Simple forms work fine.
We were able to do a simple cam-lock.
Your real problem is lack of control over the torque being used.
An insert is G10 should be very robust.

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P.E. Metallurgy, consulting work welcomed

 

[btrueblood]

What rothers said, but maybe something from the Penn catalog? Some reason you can't have metal (insert head) on the far side of the part?

Like Ed said, threads in Macor would be tricky (might work with a CAM program and thread mill?), and I would doubt they had more tensile strength than an insert in G10.

 

[3DDave]

There are oversize keenserts for when the first size rips out.

One time we had a problem because there was a gap so the bearing of the mating part was not on the insert and the assemblers, not feeling the bolt stiffen up, would just keep turning. These were large fittings with cross pins to hold them in an epoxy pocket. After a discussion that it was not required to fully torque a joint for in-process transportation that at the end was going to get peelable shims to fill the gap (which were helpfully dangling in a bag tied right next to said bolts) the rather expensive rework was no longer required.

 

[TugboatEng]

Keen-serts don't have fully formed threads on their OD. They use an oversized drill for the tap size. It is meant to make drilling and tapping in the field (hand tools) easier. This is probably contributing to your pull-out problem. The Mil-Spec keen-serts do have full thread profiles. Are you using the correct keen-sert? Have you looked into inserts specifically for composites? Take a look at Click-Bond.

 

[MintJulep]

Could you change to a thermoformed use thermoset material?

That would open up a lot of insert options.

Molded in, heat installed, vibration installed

 

[TugboatEng]

This is the standard keen-sert thread form by the way. Notice the flat troughs in the threads.

 

[drawoh]

TugboatEng,

The drawings I have call up tapped holes. The parts have what I identify as Keen-serts. I have no part numbers. We are going to centrebore, and install PEM broaching nuts from the opposite side.

--
JHG

 

[Tmoose]

How thick is the G10, and how large are the fasteners ?
that is, how many "diameters" of engagement are possible with yoor G10 thickness?