What size holes to drill in bar?

[Mekanizm]

For a CSM I am going to make that I bolt on to the bar. Maybe two holes near the powerhead and one in the center of the tip.

I would imagine it is either for a 5/16" or 3/8" bolt.

So what size holes should I put in?

Thanks

 

[TSRuff]

All of my bars have two holes hear the powerhead and one through middle of the bearing at the tip. All are 1/4" and I've never had a bolt of this size break or show any signs of wear.

The smaller the hole you can get away with the better as you will be drilling through some very hard steel. Searching for "bar drilling" will get you some good threads on the subject, but I normally use carbide masonry bits on the drill press with it set to as low of a speed as possible, steady pressure and about 10x more lube oil than you really think ought to be necessary.

Plan on using up about one bit per hole...

 

[sdo]

I have kept all the bolts on the mill I just made 5/16" that way I can use the chainsaw tool on all of them (no need for more tools in the field)

I was worried when it came time to drill my bar (everyone says its such hard steal) but the 2 holes I drilled in the bar (motor end) where easy to drill. Started with 1/8" then 1/4" then 5/16" slow speed and oil on a drill press. No problems. I can see the centre of the tip being harder, but I only single end mounted my bar so I never drilled it.

 

[devonhubb]

I drilled a 5/16" hole in the center of the sprocket nose bearing, and one 5/16" hole near the powerhead. Seems to be working well for me.

 

[BobL]

I use 8 mm (5/16) on the bar and 1/4" or 5/16" on the nose and 3/8 when I used to drill holes for Aux-oilers on hard nose bars.