slot mortiser


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I am building this slot mortiser.


I even preferred to buy the track precut from these guys.


Now the problem, the track is not predrilled and I can drill the aluminum track, but the heads of the screws must be counter sunk for the bolts to slide in the track.  None of my counter sinks will fit into the track slot to allow me to counter sink the heads so the screws will allow the bolt to clear.


Looking for suggestions on how to countersink the holes without going through the material.


Thanks for any help.





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The right profile of drill bit can sometimes work. Drill your through hole and then an appropriate bigger bit to fit.

It is not ideal.  A drill bit is around 118 degrees or 130 degrees at the tip, the right angle for English flat head screws is 81 degrees and 90 for metric.  Especially screwing into metal you would want the right angle as it will not be as readily compressed as wood.


Opps that should be 82 degrees not 81 degrees.

Edited by ponderingturtle
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Sorry, I never use that screw profile. Lots of others. And yes, I already admitted the sometimes because with my offer the thickness of material matters. The concern is a channel too narrow for a purpose built countersink. It is going to require some sacrifice if a countersink cannot be found that will fit. I see you don't like my workaround, what is your path?

Get a 1/4" countersink.  They make them, and they are perfect for this. They also make long reach ones.


I also added a link to it with a double ended 1/4" countersink from mcmaster carr that should be perfect and give two sets of cutting edges.


There are longer countersinks but that probably wouldn't be needed with the depth here.


You can also get 82 degree center drills that would do the job


That would deal with any length you needed and it goes down to a 1/8" countersink.

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Here is a grizzly set that has an 82 Degree 1/4" Countersink


If you go with something like an M3 screw this would work  Though it is not intended for metal unlike other countersinks.

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