Engineeringtech
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- Joined
- Jul 29, 2013
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Hi everyone. Anyone here know about shrink fitting cutters and drillbits into steel shafts?
The other day I needed do drill some very accurately placed, .147" diameter holes in a cast chassis with tall (3") side walls. As some of the holes were located within 3/8" of the side walls, a jobber length drill wouldn't reach without the chuck striking the wall. I had some taper length drillbits, but they weren't split point, and drifted when I tried to start them. I couldn't drill from the bottom side of the chassis, because my reference points were on the inside.
I decided to make a drillbit extension. I had a split point, screw machine length drill in .147" diameter and some 1/2" diameter shafting that ran very true in my lathe. I would drill the end of the shaft to accept the bit, and setscrew it into place. But then I thought I had a better idea. Some companies attach their cutters to tool holders by shrink fitting them. (I've never done it, because all we have is R8 tool holders.) Closest reamer I had was .145". So I drilled a .136" hole, then reamed it to .145" (1" deep). I blew out all the chips, and while the spindle was turning, heated the drilled end of the shaft with a torch. I figured that would prevent the shaft from warping. Once I got the end of the shaft dull red in color, I stopped the spindle, and quickly drove the shank of the .147" drill into the hole using the tailstock chuck. Unfortunately, the shank only penetrated about 1/8" and stopped. It doesn't run very true.
Was the .145" hole just too small? Or should I have heated the shafting more? Or is this just a bad way to make a drillbit extension?
The other day I needed do drill some very accurately placed, .147" diameter holes in a cast chassis with tall (3") side walls. As some of the holes were located within 3/8" of the side walls, a jobber length drill wouldn't reach without the chuck striking the wall. I had some taper length drillbits, but they weren't split point, and drifted when I tried to start them. I couldn't drill from the bottom side of the chassis, because my reference points were on the inside.
I decided to make a drillbit extension. I had a split point, screw machine length drill in .147" diameter and some 1/2" diameter shafting that ran very true in my lathe. I would drill the end of the shaft to accept the bit, and setscrew it into place. But then I thought I had a better idea. Some companies attach their cutters to tool holders by shrink fitting them. (I've never done it, because all we have is R8 tool holders.) Closest reamer I had was .145". So I drilled a .136" hole, then reamed it to .145" (1" deep). I blew out all the chips, and while the spindle was turning, heated the drilled end of the shaft with a torch. I figured that would prevent the shaft from warping. Once I got the end of the shaft dull red in color, I stopped the spindle, and quickly drove the shank of the .147" drill into the hole using the tailstock chuck. Unfortunately, the shank only penetrated about 1/8" and stopped. It doesn't run very true.
Was the .145" hole just too small? Or should I have heated the shafting more? Or is this just a bad way to make a drillbit extension?