Spotting drill- angle tolerance question.

[JDana]

What should I expect it to be?

My customer print called for an 82 degree spot face, plus/minus 1 degree. We needed a special diameter and requested our supplier grind down an off-the-shelf carbide spotter. Supplier decided to make our spotters from scratch, using plus/minus 3 degrees!!! I said no way. He claimed that's standard. I still say no way!

Internally we have some people that would accept plus/minus .5 degree and others saying plus/minus .1 degree based on the 10 to 1 inspection rule.

What about the angle of a step drill used to eliminate the spotting drill? I think it would be the same, no?

Thanks to any help.

 

[MikeHalloran]

I thought stock spot drills were 90 degrees.

BUT... if you bought a total custom part, it would have been better to make a drawing, with tolerances, so there would be no argument about what's "standard".



Mike Halloran
Pembroke Pines, FL, USA

 

[looslib]

Countersinks are either 82 degrees, inch parts, or 90 degrees, metric parts.

Spot faces are usually perpendicular to a hole to provide a flat surface for a washer, nut or bolt head to set flat on.

What is a 82 degree spot face?

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
Sr IS Technologist
L-3 Communications

 

[JDana]

Of course I should have said 82 degree countersink as opposed to spot face. And thanks for the reasoning behind 82 vs. 90, we do both and I never realized why

The tool wasn't considered to be a total custom piece, I just wanted a stock spotter turned down about .050" for clearance issues.

I wonder about standard because tighter than standard generally costs more and our next tool will be a custom made step drill.

Thanks again.

 

[MikeHalloran]

A spot drill or spotting drill is a short fat drill with a fine point, often thinned. It's used in CNC machines to start a hole, e.g. penetrate a few mm and leave a conical recess to guide the actual hole drill, where the hole drill is too slender to start the hole without walking. The o.d. is not normally used. They are commonly supplied with 90 degree points because they are also commonly used like end mills for chamfering straight edges.

Other angles are possible, of course, they're just not common. If you actually have 82 degree spot drills, please call them that, not countersinks and not 'spotters'.



Mike Halloran
Pembroke Pines, FL, USA

 

[JDana]

Mike,
My first post used the terms "spotter" and "spotting drill" both refering to the same tool. to-ma-to/to-mah-to

My second post used the term countersink to correct my mis-use of the term spot face, both of which were refering to the feature not the tool. to-ma-to/po-ta-to

Regardless of the terminology used, I believe it's fairly easy to see that the question boils down to:

What is the standard tolerance that should be expected on the angle of one of these tools?

Thanks

 

[ietech]

See if this helps --- I Googled for countersink tolerance and got a bunch of choices.

Here is one.

http://www.guden.com/countersink.htm

 

[MikeHalloran]

I'm not aware of a standard tolerance for cutting tools. Clearly, you and your friends and your vendor disagree about what "standard" means in this application. Even if there were a universal standard, it wouldn't matter because you didn't refer to it in your contract with the supplier.


First, recognize that because the lip may not be exactly radial, the angle measured on the tool may differ from the angle it produces on the workpiece.

But that's not your biggest problem.

Since you didn't specify otherwise, the standard tolerance is whatever your supplier says it is.

The "10 to 1 inspection rule" deals with the necessary resolution of inspection tools, >>>_relative to the specified part tolerance_<<<. Since you didn't specify a tolerance, again, the tolerance is whatever your supplier says it is.

Plus/minus 0.5 degrees is a standard default tolerance in the title block of many companies' drawing sheets. Since you didn't fax a sketch of what you wanted on a sheet with such a title block, and since you didn't fax a sketch at all, the tolerance is whatever your supplier says it is.

If your supplier publishes a catalog, that may define his standard, which he may be mis-quoting. If not ...

... pay the supplier's bill and learn a lesson.

I suggest that it should be SOP to follow up a phone order with a sketch or drawing, specifically carrying:
- an image, however crude, and
- dimensions to show what you want, and
- tolerances to specify what you will not accept.

In the case of something like a cutting tool, it's probably better to just define the important interfaces, i.e. the cut in the workpiece, the shank of the tool, and any clearances that need to be maintained, rather than telling a supplier how to design a tool. You still need the tolerances on the interfaces.



Mike Halloran
Pembroke Pines, FL, USA

 

[eromlignod]

If it's for a standard flat head screw (and it sounds suspiciously like it is), the ANSI standard for the screw itself is 82 +/-2 deg. If it is indeed intended for a screw, I don't see any need for the c'sink to be any finer than the screw.

And, for what it's worth, around here a "spotface" refers to a flat region around a hole for a screw head or washer to seat on, like you would machine on a casting. The stubby, combination drill and countersink tool that Mike refers to, we call a "center drill", as it is often used in the tailstock of a lathe to start a pilot without walking and to make a center hole to couple with a live center.

Don
Kansas City

 

[MikeHalloran]

Uh, no, Don. A center drill and a spot drill are different.



Mike Halloran
Pembroke Pines, FL, USA

 

[eromlignod]

I re-read your post and now I see what you're talking about. It sounds like what we call a "starter drill", which is just a drill bit with a 90 deg. tip and short flutes, for making an indentation. I don't think they would be very appropriate for milling a chamfered edge, though. For that our machinists use a "drill mill", which is an entirely different tool, made more like an endmill.

Don
Kansas City

 

[unclesyd]

The good old 60 degree center bit.

http://www.littlemachineshop.com/products/product_view.php?ProductID=1230

Reamer bits

http://www.grainger.com/Grainger/categories/metalworking/drilling/center-reamer-drill-bits

Countersinks of varying degree.

http://www.ostartools.com/products/formetal/countersink/countersinks.htm