Bob Hull wrote: > For drilling pin blocks, I am re-evaluating the drill bit size and procedure > that I have been using. The last few blocks I have done were composite blocks > multi-lam with 9 mm delignit cap. I am double drilling with 1/4" then an F bit > at about 2340 spindle speed, usually yields about 160 in. lbs. for the sample > pins that I try in a scrap piece of the block. I would like to get about 180 but > I can't get that with the F bit. By the time I get coils just right, chip and > tune for a year, the torque is not as high as I would like. I have a block > in the works now (already drilled the 1/4" hole) and I am going to get a 6.5. > mm bit today and try that on a sample. I got a new drill press after my last > one seemed to have too much slop in the quill but the repair people said it was > within specs. I just got a table top delta. I am keeping the humidity in the > shop now in the low 40's. (The block itself stays in a 35 % rh environment when > not being worked on.) > > What beginning torque do you like to see? How much do you expect it to drop in > the initial stages? Hi Bob, I drill 1/4", and 6.8mm at 1250rpm and get in the 160-170 range. A year later, they're in the 150-160 range, or thereabouts. My old radial drill press has plenty of quill slop, and I don't see that making a bit of difference. I don't expect going 0.03mm smaller on the bit will make the difference you're looking for either. It's been a while, so I've attached a spreadsheet with data supplied by Mike McCoy. Note that torque is material dependent to a certain minimum hole size, and a smaller hole doesn't appreciably affect torque readings. Looks to me that if you want more torque without losing the benefit of the composite block, you might use Falconwood for the cap instead of Delignit. Ron N -------------- next part -------------- A non-text attachment was scrubbed... Name: pinblock2007.xls Type: application/vnd.ms-excel Size: 66048 bytes Desc: not available URL: <http://ptg.org/pipermail/caut.php/attachments/20100729/14b54b83/attachment-0001.xls>
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