View Full Version : How to drill INTO the end of an endmill?
02-08-2008, 11:30 AM
I want to make an inexpensive crown cutter for some older gun barrels that I can't fit into my lathe for various reasons.
I figgered I could drill a hole into the end of an endmill and add a brass pilot. Probably be easiest with non center-cutting mills or extra longs with the center hole already there. Can a centercutting HSS endmill be drilled as it is? Or should grind a small flat in the center with something like a chainsaw sharpening stone on a dremmel (in lathe)?
While I was at it, I thought a hole for a tommy bar would be an easy way to drive it. I'd cut a flat so the drill doesn't wander, and drill with carbide drill.
Your Old Dog
02-08-2008, 11:36 AM
Not wanting to sound like a nay-sayer here but unless you have a cutter with a concaved profile I doubt it will be worth your effort.
I thought the geometry of the end of a barrell was very important to accuracy in that the crown is the very last thing that the projectile sees and maybe more importantly, that the exhaust gases get to push against?
I have snapped a couple endmills and they look crystaline in structure. They just gotta be tough to drill. A grindstone may be the only way if even that will work. Good luck
02-08-2008, 11:55 AM
The crown is indeed a very important part of a rifle's accuracy. That is why I need to recut the ones I have.
There are several different ways (all correct) to cut a crown. The kind with the concave as you mention is called an 11deg target crown. The kind I would hope to cut are stepped crowns. The center is drilled deeper, almost like a counterbore. Both kinds provide a flat, concentric-to-bore, protected end of the barrel, which is paramount to accuracy.
There are several kits available and most cost over $100. They are essentially an endmill with a hole in them...such was my inspiration.
Sure I'm being cheap, but thought I'd give it a try.
02-08-2008, 12:14 PM
Anneal the endmill and then drill as you wish.
Harden afterwards. I have diy hardened a few endmills in a flame after turning them into some sort of formcutter and almost every other bit will react different to heattreatment. Just experiment. Last bit did not take the anneal and could only be used as hard as after hardening.
Being old barrels probably soft low carbon steel i doubt toollife will be a problem. Now i have got my oven i will clean up my act but this procedure has served me well.
Try a worn bit first. If in really bad state you can face the cutter in your lathe after annealing and file the relief angle afterwards. Stone after hardening.
02-08-2008, 12:49 PM
You will not be able to anneal and reharden an HSS end mill without some pretty sophisticated heat treat equipment.
You can purchase piloted counterbores that will accept a pilot you can machine to the desired size and provide a flat face. Pricewise, they are about the same as an endmill.
02-08-2008, 01:13 PM
Find you a tool grinding shop and have something made. What you want is basically a piloted counterbore with a custom ground face. If you are going through the trouble get it made from carbide, your paying for skill and labor, not materials.
I think if it wuz me I'd take a piece of drill rod and make what I wanted. Or look into Jim's idea of adapting a piloted countebore. Drilling a HSS end mill does not strike me as a practical proposition.
02-08-2008, 01:31 PM
Brownells has several barrel crowning cutters, such as http://www.brownells.com/aspx/ns/store/ProductDetail.aspx?p=628&title=79\%20MUZZLE%20CROWNING%20CUTTER
You can just buy the basic cutter and make pilots to suit what ever rifle you are working with. Look at the revolver chamfering kits, they have a flat facing tool, you can always grind off the OD of the cutter to get it to the dia you want.
Also, as a previous poster said, look at counterbores such as this page in MSC catalog:
They cost from $20-30 for import types, you make an insert to do what you need.
02-08-2008, 02:21 PM
Find a tool shop nearby - preferably die casting for aluminium or plastic - and they should have an electro-erosion machine. That thing will drill the hole for you.
And I was just thinking the very same thing today - I have an old barrell, my Logan will not hold it, and I would like to recrown ti too.
02-08-2008, 03:31 PM
If the crown isn't to dinged up, I've done some very nice touch ups with a round head screw and valve lapping compound.
(Idea stolen from Brownells "Gunsmithing Kinks")