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Tolerances Suitable for Tool Diameters

Tolerances Suitable for Tool Diameters

Tolerances Suitable for Tool Diameters

Can anyone point me to a reference for tolerances applicable to diameters of mills and drills?

I know I can conjure up something that will work using max, min, or limits. I'd prefer to use tolerances based on a long history of general use and standardization than tolerances I pull out of my hat.

A quick search of IHS didn't turn up a title that looked appropriate.

Jason C. Wells

RE: Tolerances Suitable for Tool Diameters

A better approach would be to specify the most generous combination of dimension/geometric tolerances your design allows. Then leave it up to your manufacturing people to decide what process/tooling is the best option. They may prefer to mill a hole rather than drilling it, since it might reduce machining time by eliminating a tool change.

RE: Tolerances Suitable for Tool Diameters

OR, are you asking for customary tolerances of the mills' or drills' shanks, or cutting edges?

Drills hardly ever cut to the diameter across the flutes, and CNC mills can easily orbit a smaller cutter to make a hole of arbitrary size, so for part design, it's best to just worry about the hole tolerance you need for the design to work, and not worry about the size of the tool that makes the hole, as tbuelna said.

Mike Halloran
Pembroke Pines, FL, USA

RE: Tolerances Suitable for Tool Diameters


Are you fabricating the tools?

If not, you don't care what their tolerances are. The Machinery's Handbook has a table somewhere showing the tolerances you should expect on a drilled hole. CNC people do not like to stop their cutters from feeding. If you specify a 10mm radius, they will use Ø5/8" cutter.

On your drawing, specify the radius and the tolerance. Let them figure out how to do it.


RE: Tolerances Suitable for Tool Diameters

CH: Yes, something like that. What book was that from?

Drawoh: I was not aware of that. Good to know. I think in terms of manual milling so learning the CNC perspective helps. I need to bring my MH to the office.

I was specifically thinking on how to specify tolerances for side milled profile corners to make it easy (inexpensive) for a shop to produce an acceptable part. Based on the input here, I was chasing after a false economy. It's better to just spec the part I need and let the shop figure it out.

My office likes for us to use our tolerance blocks as much as possible. I wanted to be sure "default" will work with run of the mill tooling. The page that CH linked gives me confidence that tolerance block tolerances are going to be OK for almost every case.

I know engineering is not supposed to tell a shop _how_ to make stuff. Evenso, I do try to keep the shop in mind when detailing parts.

Jason C. Wells

RE: Tolerances Suitable for Tool Diameters

Tolerances for cutting tools can be found by using DIN. DIN 1420 for instance gives the manufacturing tolerances for reamers. There will most likely be a ISO number for DIN 1420.
Once you know what kind of cutting tool you want to produce or buy than you can find all your info under the DIN for that particular tool.
For instance, a certain end mill will be made under DIN 844B, type N. By looking up that DIN you will find all the info for this cutter. Schaft, Flat, dia, material etc. There you will find reference to cutting angles, clearance, tolerance and all that is needed to make this cutter type.
I am certain there must be a similar system for inch based cutting tools.
Find a catalog from a large manufacturer of cutting tools like Guehring and you can get most info for free in the technical section. Otherwise you will have to buy some DIN hand books.

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