Greetings! I'm planning to use some steel racks (20 pitch) from McMaster for a CNC project. Problem is, they are not drilled and tapped (pre-drilled & tapped racks seem to be about double the price). The racks are 1/2" x 1/2". I'm thinking #10 mounting screws. The holes are blind, going into the back of the rack. The racks are pretty hard. Any advice on getting this done without ruining a bunch of taps and - worse - racks? (I thought of brazing studs into plain drilled holes, but I'm afraid this would warp the rack and make them soft and prone to wear.)
Tapping a rack
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Try making clamps
If the rack is hardened you might be better off clamping the rack in place rather than the frustration of losing a few taps becauise they break...
Multiple clampng points will hold it in place well and you could use 1/4 or better yet 5/16 bolts and it will never move.
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Are you building a Mechmate? They use the same size and pitch and get away with 3M double sided stick tape. http://solutions.3m.com/wps/portal/3M/en_US/VHB/Tapes/
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Id tap that rack! err no wait.
How about drilling through the side of the rack? I my lathes rack is held in place by bolts into the side of the rack and held in location by roll pins.Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.
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Offhand, I'd have to say that if you can drill it with hss or carbon drill bits, you should also be able to tap it. Tapping blind holes is not my idea of fun, especially in a hard material, so if you can live with a few holes going right through, between teeth- consider what size of bolt you could use that wouldn't require the tap to thread up more than a bit of the root of the teeth. Tap right through, then check the length of the bolts that you finally use, and keep them a tad shorter than the roots. Use stronger bolts if the diameter of them gets too small. SHCS perhaps. Pretty strong even at 4-40, and it appears to be your option as to how many you use.
On the other hand, if you can drill the pilots just short of coming through, and that leaves enough hole that you can get in say four or more good threads, you could always just epoxy some studs into those. They would only go in maybe an eighth inch or so, but that could be ok.
You could always do what I've had to a few times- screw in a bolt as you go along threading, and stop when the bolt can thread in just past where it would need to in the final assemblage. Did that just yesterday to save on frustration when tapping a blind hole. It's nice to have some room left at the bottom so the tap doesn't get too hard to turn.
One thing keeps flashing a mental led- how else are you supposed to be able to mount these racks?
If you find that you can't tap the material-Last edited by darryl; 01-28-2010, 04:34 AM.I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-
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Tapping a rack
Thanks for the ideas, guys!
I'd like to drill straight through side-to-side, but unfortunately the sides of the rack won't be accessible in this particular design. I've wracked (he, he!) my brains, and can't get around it.
Never thought of double-sided tape! Would probably work fine, but the thought of leaving an automatic machine unattended when one of the racks is secured by tape gives me the heebie-jeebies.
Clamps: I'll have to think about that. Problem is, there isn't a lot of room around the rack (that's why the sides aren't accessible).
Darryl: looks as if the end of your post got cut off.
Again, thanks for the input. J
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alsinaj,
Just to let you know Shopbot uses double sided tape to mount their racks as well as other manufacturers. They all had the same problem. You could weld them into place if you dont feel to comfortable about the tape but here is a link to others that have build large professional machines that all used double sided tape as well. http://mechmate.com/forums/showthread.php?t=751
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Hmm, I got cut off- probably cut myself off somehow. Anyway I was going to suggest maybe grinding some grooves in various spots on the sides so you could insert the edge of a washer or something to bolt it down with.
Something else that comes to mind- do you know anyone who will spot weld for you? Spot weld some sections of threaded rod on the back for mounting studs. The momentary heat won't penetrate far enough through to affect the heat treatment.
Then there's friction stir welding, where you force the rotating stud against the back of the rack until it welds itself on- never tried it myself but I'd like to.I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-
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How about bolting the racks through the side to an L bracket?Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.
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