Modifying a hole saw arbor to make a double hole saw

[Frank S]

TO do this make take making several special tools
I started off by grinding a holding flat on an extended length 1/4" drill bit. So I could mount the arbor on it upside down, the reason why will become apparent after a few more tools are made

Next I reamed a 3/8 flat washer to fir over the 7/16" 20 thread

Next I put the large diameter hole saw on the arbor and used 2 5/8" hardened washers as shims. The only reason I used hardened washers were they are consistent in thickness and had just the correct stack up thickness, then I placed the reamed 3/8 washer over these. This would allow the small diameter hole saw to serve as the locking nut to hold the large hole saw

Next I had to make a thread insert because the 3/4" Dewalt hole saw has 1/2-20 thread and the arbor has 7/16- 20 thread
to make the thread insert I used .032" soft mechanics safety wire.
I chucked a 3/8 bolt and the wire in one of my lathes then with the back gear engaged I ran the lathe in reverse to make a spring out of the wire


I then installed the wire spring in the small hole saw

Then tightened the hole saw on the arbor making a double hole saw for making washers out of brass shim stock

This shows the assembly from the rear