Drilling question .25 hole is not .25? why

[dertsap]

i didn t realize those were meant to be precision holes , i suppose i'm in the habit that if it's marked fractional then the hole size is generally +-1/64 or some sort of open tolerance

speaking of carbides , garr makes a nice 3 flute carbide drill that works great on mild steel ,i used to use them on production parts with a tolerance of +.0005 , we'de run thousands of holes in 1018 with a 1/2" dia drill 1/2" deep with a nice finish , i honestly don t think people take enough advantage of those types of drills

[Mike Stevenson]

Originally Posted by Rich05 I want a tight fit for a 1/4 shoulder bolt to slide through.

Not a lot of slop there.

[dertsap]

oh ya there we go , wasn t paying attention to the shoulder bolt thing

[Palerider]

Tight fit, little loose, wish I knew what was dimensionally needed.

[Mike Stevenson]

Size, Roundness, and Cylindricity.

[Palerider]

I am familiar with those terms. I always have numbers with which to associate them to our reality when called upon it make a hole.

[Mike Stevenson]

Originally Posted by Palerider I am familiar with those terms. I always have numbers with which to associate them to our reality when called upon it make a hole.

Indubitably.

[youngjim]

Originally Posted by Rich05 Drilling mild steel making 1/4 holes and 3/8 holes it seems the holes are allways a bit oversized. The bolts have a bit of slop in them. If I want a tight fit for a 1/4 shoulder bolt to slide through should I be using a smaller drill? Does the hole come out a bit wider due to vibration/chip removal? Going through about 1" of steel the shoulder bolts have threads on the exposed end. Using a CNC machine to drill the holes, new carbide drills, very slow feed rates, and slow spindle speeds (300-500 rpm). Thanks R.

Check your bolts, too; I wouldn't be surprised if they're a whiff undersize.

[Rich05]

[QUOTE=Mike Stevenson;474415]What brand of drill are you using? not sure of brand says Co. USA about $6.

What speeds and feeds do you use? about 2 ipm

How deep and how many holes do you get from one drill? 1" 8 holes
Flat stock or cylindrical? flat

How many do you break? bent one while alligning part..

You say the size is good but how about the True Position and the Metrics? no sure what this is.

What is the hole size tolerance? not sure .001? just so bolt is fairly tight



Mike I have not resolved it yet. just gave the fellow the parts. but need to know for the next time.

[DareBee]

.001 tolerance?
You can't get much easier than drilling and reaming.