I am installing a Tom Morris suspended B/C the 1/8" post supplied (3.19 mm) fits perfectly through the B/C. The B/C mounts I installed I drilled with a 1/8" bit..BUT the post won't go through, the hole is just a tad to small. Redrilling with a 9/64" bit gives it to much slop, is there a bit size made for the 3.19 mm post or I really don't want to get a round file and mess with that way of fitting. I haven't called Tom, figured he's to busy and that some one here would know..

Thanks

Thanks Mike, went to True Value and picked one up..

For critical holes, I usually drill slightly undersize, and finish with a round needle file.  You can get exact size that way.

If you're drilling wood and you're not a Super Machinist that's probably the only reliable way.  Anything that's got a lot of give to it (like wood or plastic) will tend to leave you with a smaller hole than drilling into steel.

I'm going to contradict myself: you may be able to do this by drilling undersized, soaking the hole with thin CA to make everything more rigid, then drilling it out with a 1/8" bit or a #30.  You'll have to do some experimentation and there'll probably still be some variation, though.

I used the # 30 bit and all is well.. thanks again. I also marked it so I'd know it's size.

Mike H

I dunno...sir....(responding to your emoticon)

I have a good set of calipers .001 and a fairly expensive set of drill bits from teeny tiny (#60) up to 3/4"

I mike the piano wire or rod for the bell crank...find the exact same drill and the hole is always too tight in BC materiel ( aluminum, Delrin, PC board, Nylon, Phenolic) and too loose in Ply wood

MY drill press does have some measurable run out but not horrid

I frequently deliberately drill under sized and use a round needle file to get the fit I desire


Jest sayin

Makes me think of the commercial with Tarzan and Woman !!! 

Spent $$$ on a drill press.. spent $$$ on drill bit's, suppoase to be 1/8" wire used 1/8" drill bit  hummmm 

Music wire is generally a bit oversized, so if that's what's being used, then the "1/8 inch" stuff is probably a bit bigger than 1/8".

For a critical hole I use the correct size drill.  You don't have to be a "super machinist" to make a hole in wood, just the right tool.  A 1/8 drill will make a 1/8 hole, unless you've done something wrong.  A file?

No. Typical drill bit tolerance is + 0/-.003. Reamer tolerance is typically + .0015/- 0. Even with a .125 drill bit (measured) used to drill a hole in metal will not give you a hole that a part will slip into. In full size aircraft work, 1/8" fasteners almost always call out a #30 hole unless you can drive the fastener in. That's .0025 or so difference in size.

Typical dial or vernier calipers are accurate to .0005 and can be used to measure drill bits and rods just fine. The main thing is the comparative readings. If the rod measures .125, you normally need a bit .003 larger.

Truly "critical" holes should be reamed for a line-to-line fit, which is 0.00 +.0005/- 0.00 as compared to the part being installed in the hole.

Just sayin'.......

I would have suggested burnishing the hole in plywood with a piece of the 1/8" music wire, preferably in the drillpress. Grind or buff a little chamfer on the end of the wire to get it started in the hole. Don't use too much rpm or you might start a fire.  Steve