[hatchmar]

We are looking for they best brand/type of tap for machining AR500 plate steel- the size is 3/4-10 and pretty much everything we have tried is just shattering taps- tried to slow down/speed up SFM, tried "peck tapping" (one rev then clean off) tried different styles of taps (i am not exactally sure which ones they tried but none have worked so far)

we have had pretty good results from Emuge on a514 which is around 250 brinell but the ar 500 has a brinell of 450-550

one of my suggestions was to pre drill just a few thous. larger to reduce the torque but it is being frowned upon so that is out....

[keebler303]

In that size I think threadmilling would be straight-forward.

Matt

[txcncman]

What drill size for the hole prior to tapping? About 500 Brinell does not compute. What is the actual hardness? Any material over about 330 Brinell, you should probably use powdered metal taps. What actual cutting speed/RPM are you using? For a cutting speed of 25 SFM, you would be at 127 RPM.

[hatchmar]

we started with 21/32 hole size and then moved all the way up to 11/16- also i think the operator started at 110 rpm and also tried slower- around 50-75 rpm. the AR500 is abrasion resistant armor plate and it is between 470 and 550 brinell hardness... kryptonite

[txcncman]

Ok. Yeah. You are going to have to thread mill or try powdered metal taps then. That is like 55 Rockwell C. Means you matched the hardness of HSS tools.

[neilw20]

Gun taps have less flutes and a stronger center section.
As the chips cut forward with a nice action.

[fizzissist]

Have you called Emuge tech support? They've been incredibly helpful for me. Friendly and knowledgable. Saved me lots of money and headaches.

AR500 is unreal steel. Glad it's not me trying to thread it.
For your application, I'd be inclined to go with a carbide thread mill.
More expensive than one tap, far less expensive than 3 or 5 broken ones.

I do hope that when you're done you'll take the plate out and enjoy shooting at it.

[azcncnewbe]

I am milling tapered holes with a 800-5000 1/2 hot mill air cooled 58.00 ea on 1" thick AR500 its done in a in1 1/2 mins,

[danaman]

I mill ar500 steel at 15,000 rpm on a cnc router.