I'm repairing the connecting rod of a small steam engine. The diameter of the pin is .1875 but the hole is worn oversize. I want to make a new pin about .195 and ream the holes accordingly. I remember hearing about something called a D-bit. Would this do a good reaming job in bronze? Can someone please refresh my memory as to making one? Engineman1
It looks very much like a round boring bar, with half the diameter ground away at the end. There is only end relief, plus maybe a slight angle on the end's cutting edge. The corner between the side and end cutting edge is slightly rounded. The end relief depends on the metal being cut--for brass or bronze, probably close to 5 degrees from vertical. A D-bit is basically a single-tooth reamer, so it doesn't automatically align itself with a hole the way a multi-tooth reamer does until after it enters the hole enough to get past the ground-away area of it's tip. So to avoid bell-mouthing, you need to align the work and the reamer in a solid setup using a lathe or milling machine.
Ken Grunke
Wouldn't it be a lot easier to just buy a 5mm reamer off the shelf, ream the rod and piston and then make the pin to suit whatever size the holes actually came out?
John -
Check out page 29 in the www page of mscdirect Nice picture. page 29 bottom and 30 top contains their sizes but the picture is on 29.
Martin
Thanks but no thanks. I'd like to learn how to make my own D-bits because I sometimes have a need to ream odd sized holes. I googled for D-bits and got over 200 hits.There were contradictions in what few instructions there were for making one. Some suggested that all you had to do was turn a piece of steel to the desired size, mill or grind the end to 1/2 the thickness and harden. Someone said that the flat end had to be .001" thicker than half the diameter. Others talked about using a pilot diameter and cutting a groove at the transition point. There were suggestions about hand filing a cutting edge but nothing about angle or location. After all that I feel like I know less than when I started. Engineman1
---------- Guy Lautard has a good artical on making D-Bit reamers. Machinist's Bedside Reader, page 52. Also the Home Shop Machinist book, The Shop Wiscom of Frank McLean has a 'how to" no D-bits on page 222. Regards. Bob G. _AT_ = @, _dot_ = . to eMail
I have also used as a reamer a piece of drill rod of the correct size with the end ground flat on a long angle. Or hollow ground.
John Martin
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