Drilling Thompson Linear Shafting

[MikeAber]

I would like to add support to some existing linear shafting on my mini gantry mill.

Will a solid carbide, 1/4" 2 flute 135 degree straight flute drill cut thru the case hardened surface?

I'm thinking I can spot drill the linear shafting then drill and tap holes for 8-32 SHCS to mount a 1/4" aluminum support rail to the 1/2" shafting.

[ViperTX]

So, the bearings are the "open style"? I suspect that you'll have to mill a flat spot to be able to start the drill.

[DLMACHINE]

I built a router about a year ago using thompson rails and I started mine with a carbide spot drill then drilled with a carbide 135degree split point screw machine drill. Had no problems.
I removed for sale item at admin request.

[FranH]

I certainly would first mill a flat to keep the drill perpendicular to the part then body drill at least .100 deep. An oversize drill to allow 60% or 50% threads will help to prevent tap breakage. Once the tap drill has broken thru turn the shaft 180 degrees and body drill .100 deep from that side then tap the threads.

[DLMACHINE]

You can't rotate the shaft 90 degrees, you would be drilling into the bearing path.

[MikeAber]

This is a blind hole operation, a ball bearing race is 180 degrees from the mounting hole. I thought I would ask before purchasing the $20.00 carbide drill only to break it on the first try. Now that I have thought about it, I'll just use a carbide end mill to get thru the case and a standard screw machine drill will work fine for the rest of the operation. The carbide end mill is only $5.00, If I break one it's no big deal, I have lots of those allready.

Thanks everyone for your comments, I'll post my results here for future reference.

[MikeAber]

I tried this yesterday and destroyed a 1/4" 4flute solid carbide endmill. I got about .015" into the case hardened shaft before the end mill edges got too dull to cut. Those rods are really tough.

[FranH]

Originally Posted by MikeAber I tried this yesterday and destroyed a 1/4" 4flute solid carbide endmill. I got about .015" into the case hardened shaft before the end mill edges got too dull to cut. Those rods are really tough.

You gotttaaaa slow down the rpm (300-500) and feed slowly by hand ...coolant or cutting oil. If you cannot have the beginning of the entrance hole and the last .1 distance at the exit larger than the tap you will find greater problems threading than you found milling. Suggest a 50% thread to take the pressure off the tap. You're right thse rods are really really really tough.

FranH

[widgitmaster]

Your best bet is a solid carbide ball end mill with 3 or 4 flutes, running at the slowest speed, then bring the knee up very slowly, keep the quill retracted to ensure rigidity too! Best done with thick brown cutting oil, as it bonds to the cutting edge under pressure and increased temp. Those rails have .09 to .125 thick case hardening, and a soft steel center.
Drill the hole for a shallow thread as mentioned earlier, to make it easier to tap, make the bore through the case about .015 bigger than the tap diameter!

[DareBee]

You guys are making this to difficult.
Take a hand grinder (dremel whatever) and grind the case off (carefully (of course)) it is about .050 deep (We usually just grind a flat, nothing fancy) and then you can centerdrill and drill with good grade standard tooling.
Nobody will see your hand ground bit when it is mounted on the T-rail.