Model Engine Maker

Supporting => Tooling & Machines => Topic started by: petertha on April 15, 2019, 01:13:44 AM

Title: Tool steel cutter
Post by: petertha on April 15, 2019, 01:13:44 AM
I'm trying my hand at making a grooving cutter from O-1 tool steel for use in aluminum. I'll post some actual pics when I offload the camera. I've got the offset shank & the cutter body turned OK. But milling off half of the cutter head & the relief angle & back clearance is kind of a fiddly PITA in the mill. I'm wondering if I should just freehand grind in the annealed state, harden & temper, then  finish the final edge? Or do you think it would be better to harden first because there is a symmetrical blob on the end (the full round cutter disc) and then do the grinding? Or is there a risk of losing the hardness of O1 will grinding more material like this? Hopefully the pics illustrate what I mean.
Title: Re: Tool steel cutter
Post by: stevehuckss396 on April 15, 2019, 01:43:43 AM
I'm wondering if your end mill has lost it's edge. I use O-1 all the time and it usually machines very easy, even with HSS.
Title: Re: Tool steel cutter
Post by: crueby on April 15, 2019, 01:47:15 AM
Grinding after the O1 is hardened is not a problem as long as you dip it in water frequently to keep it cool, and use a light touch. I have a slow speed grinder with a fine grit wheel, have dont that many times on hardened cutters. As for better to grind before or after hardening, I cannot say which is better.
Title: Re: Tool steel cutter
Post by: petertha on April 15, 2019, 02:00:32 AM
Hi Steve. Just to clarify, no particular issues milling the O1 from a removal standpoint. Its more because the cutter is kind of skinny & held in a cantilever position I was more concerned about it deflecting. the shank & cutter body is .313 OD, the neck is .233 OD. Having said this I just remembered - I milled a tiny V-block holding plate with cross straps that would be better than how I had it supported in my main vise.

Another question. I thought I would make a nice curved transition, which would be formed by side milling. For something like this (.059" groove x .050" depth) would I be OK to cut it square to half diameter? I was thinking more about this being a problem heat treating.
Title: Re: Tool steel cutter
Post by: 90LX_Notch on April 15, 2019, 02:10:35 AM
pertertha-

If this is for use as a lathe tool, I did something simular for a small internal threading tool. 

http://www.modelenginemaker.com/index.php/topic,4406.0.html

If you are in fact making this as a lathe tool for an internal groove, may I suggest angling the sides to form a "V" shape like a parting tool.

-Bob
Title: Re: Tool steel cutter
Post by: petertha on April 15, 2019, 04:40:03 AM
Perfect timing 90LX_Notch. Going to digest your post because I need a small single point threading tool as well. There are some nice solid carbide ones available but they are spendy and I would really like to become more proficient at making custom home brew tools from tool steels.

Re the grooving tool, sketch shows side relief I had contemplated, 5-deg for no particular reason. Re milling, I think my mini V holder will work better to halve the cutter disk blank because at this stage it is the same diameter as the shank so it stays aligned. This is my first aluminum mockup but I'll have to remember to scribe a tool line on the end while in the lathe to maintain a reference. That's the one thing I learned about the eccentric tool carrier, its not a great idea to remove the part unless you have some witness scribe lines to get it clocked in position again. Maybe a better way yet is put the part in a 5C collect index holder then I could do more operations on it. I just wonder if it would deflect & distort under milling stuck out like that?

I'd like to have the shank reduction turning with a center on the end to mitigate the stickout factor, but then I have to somehow remove that end material with the countersink dimple in it.
Title: Re: Tool steel cutter
Post by: Jasonb on April 15, 2019, 07:28:57 AM
Might be easier to do the milling cut first then turn the eccentric head.
Title: Re: Tool steel cutter
Post by: jadge on April 15, 2019, 10:55:32 AM
I'd start by milling a length of rod to about half diameter. Simply put the rod horizontally in a vice on the vertical mill and use the side flutes of the cutter. I'd then either rough mill and/or file the reliefs behind the cutting edge and to the right. Lastly I'd file the reliefs on the cutting edge itself. I might then clean up the final shape by freehand grinding. Then harden and temper. Finally clean up the cutting edges with a diamond hone. I assume that O1 is a straight carbon steel, like the UK silver steel or gauge plate? Both machine well in the unhardened state. They can be ground after hardening but you don't need to get them very hot to destroy the hardening. So I prefer to shape before hardening and just do a fine hone afterwards. It doesn't really matter if the tool doesn't look pretty as long as it does the job.  :o

If the cutting edge needs to be specific width it's fairly simple to remove a thou or two with a diamond hone.

Andrew
Title: Re: Tool steel cutter
Post by: Mcgyver on April 15, 2019, 01:05:18 PM
I've always machined to the shape I want, then heat treated and finished the edge with a stone.  You won't draw the temper that way, and machining it annealed is easy