Mortising - Too much pressure?

[chipmaster]

I have a mortising attachment for my Delta drill press and, now, one that came with my 10ER. If I can get the 10ER one working right, I'll sell the Delta one. Problem is, as currently set up it requires tremendous pressure to drive the mortising chisels, so much that the table deflects. This deflection occurs with the single, old Shopsmith 1/4-inch chisel that came with the 10ER and with the brandy new Chinese 1/4-inch chisel I had bought for the Delta. Should it require so much pressure to drive the chisel? If not, is it a sharpening issue? If so, do I need one of those extra tube clamps Skip Campbell shows in his video (haven't actually checked to see if that's where the deflection is occuring)? Any advice appreciated, including any tips on sharpening mortising chisels.

v/r,

Rick

[beeg]

Mostly, the chisels DON'T come sharp enough. Are ya SURE ya have them set correctly?

[chipmaster]

I'm not sure about anything--total novice at mortising. I've been reading my "Power Tool Woodworking for Everyone" and planning to try sharpening my chisels and adjusting the setup.

Straight from the bible: "Excessive pressures are never necessary." pg 93. It's a darned handy book.

v/r,

Rick

[foxtrapper]

My experience using a Delta mortising machine is that while pressure is required, it's not "tremendous" by any means. More on par with using a drill press on steel.

You mention you aren't sure what you're doing. Lets make sure you're using the tool correctly. The drill bit needs to extend beyond the box and drill the hole. Then the box presses down, slicing the square shape.

If it's plunging correctly, lets make sure you're using the right bit. It should fit the hole, but not rattle around grossly. Don't use an undersized bit.

And then make sure the box cutter portion is sharp. Including the tips. Those get smooshed real easily when dropped.

[pennview]

You can place a length of 4x4 or 2x4 between the table and the floor to prevent the deflection of the table. This works for heavy drilling as well.

Both the drill bit and the square chisel need to be sharp. I have a Chinese-made set that really can't be sharpened well enough to actually cut mortises in hardwood. But I have some made in Taiwan that I got at a Grizzly close-out sale and they work well. I think the ones sold by Grizzly now are from Japan and should be of good quality. Shopsmith chisels are high quality and they also carry cone-shaped stones for honing the insides of the square chisels.

You need to sharpen the outside of the square chisel on a fine honing stone. For the inside, I use a Dremel with a tear drop shaped small, very fine stone. It appears to be a rubber bonded stone with the abrasive grit embedded in the rubber. Not sure where it came from but it does a nice job.

For set-up, when you insert the square chisel into the holder, don't push the holder all the way into the receiver. Use a dime to prevent the chisel form seating in the holder and gently tighten the set screw. Then install the drill bit as far as it will go through the square chisel and tighten the drill chuck. Then seat the square chisel into the receiver, closing that small gap that you left earlier. This ensures that there is a gap between the chisel and bit which is necessary for proper operation of the mortising chisel.

[dusty]

I have repurposed a couple screw jacks that were in my travel trailer. They now have a purpose in the shop - to stabilize the main table during drilling and to stabilize the outboard end of my router table.

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[wallpaperman]

I have a mortising attachment for my Delta drill press and, now, one that came with my 10ER. If I can get the 10ER one working right, I'll sell the Delta one. Problem is, as currently set up it requires tremendous pressure to drive the mortising chisels, so much that the table deflects. This deflection occurs with the single, old Shopsmith 1/4-inch chisel that came with the 10ER and with the brandy new Chinese 1/4-inch chisel I had bought for the Delta. Should it require so much pressure to drive the chisel? If not, is it a sharpening issue? If so, do I need one of those extra tube clamps Skip Campbell shows in his video (haven't actually checked to see if that's where the deflection is occuring)? Any advice appreciated, including any tips on sharpening mortising chisels.

v/r,

Rick

HI Rick, have you looked at this http://www.shopsmithacademy.com/SS_Arch ... ng_Pt1.htm

[chipmaster]

Lots and lots of helpful tips and information from you guys--Thank you! I will report back the results next time I start fiddling with the mortiser again.

v/r,

Rick