Critique my flycutting results

[Bob Korves]

Are there LH and RH cutting flycutters?

Symmetrical fly cutters with horizontal tool slots work in both directions. I have several. Fly cutters are also fairly easily shop made in whatever direction you prefer. Making a one off custom cutter for a particular job can be worthwhile, and it will likely also be used later on other and different jobs. Can't have too many!

 

[MrWhoopee]

I have a similar fly cutter. The head of mine is 2.5 diameter. Using 80 SFM cutting speed for 1018 and the tool sticks out 1/2 inch, 80 x 4/3.5=91 rpm.
(cutting speed x 4/ diameter). While it won't contribute a lot to your cutter grinding skills, I recommend a brazed carbide tool for this application.
The higher rpm range gives better finishes, particularly in 1018.

 

[chris.trotter]

I took another crack at this on Saturday, it did not go well, haha.

This was the first re-grind I attempted. The second I did not get pictures of, but I tried to get it looking like the one BillH posted. Both failed pretty badly. Ran out of time, and I'm out of the country on business this week, but will give it another shot on the weekend.

I have a bunch of spare lathe tooling that I will see about putting in the flycutter, but my real problem is that the machine vibrates and generally goes bananas when you turn it past 1/4 speed. (possibly due to it not being bolted to the countertop)

Dented but not daunted.

 

[epanzella]

Based on your description of chips AND dust it sounds like part of the edge is cutting and another part is rubbing. Seems like you're close but no cigar!

 

[chris.trotter]

Round...3?

I found another view of cutting geometry online, tried it. I think the key for my brain is to have a very clearly laid out grind geometry, those examples seem to serve me best. This attempt cut wayyy smoother, but left an unpleasant surface finish.

Speed was low (due to the size of my machine), very low (200-400rpm?) speeds are the only ones that won't start resonating or vibrating the entire machine too much. Feed rate was very slow, used oil to lubricate. Chips looked much more like "normal" chips - did not notice any dust (although maybe the oil absorbed it?).



And here's the result:


Thoughts?

 

[mikey]

Chris, go to post #9 and look at the bit that Bill showed you. This is a left hand turning tool shape that works well in a fly cutter. The shape of your cutter in post #25 is not going to work well. You must have relief angles under the side cutting edge and you need side and back rake as well as a decent nose radius. The tool in your post is just going to hammer at the work piece so yes, you can expect vibration because the tool is not cutting.

Go here and look at this thread: https://www.hobby-machinist.com/threads/how-to-grind-a-hss-turning-tool.52581/. The tool in the article is a right hand tool. You need to grind a mirror image of that tool but the process is exactly the same. Stone a 1/32" nose radius on it and the tool will cut well for you.

 

[chris.trotter]

Yeah, I feel like I might be coming across as obtuse - I looked and pondered at that pic, but my brain couldn't figure it out. Will look at that post and try again today.

 

[chris.trotter]

I have made two more attempts at this. The first of these gave identical results - I think because the radius was too large, and the relief angles too shallow. It ended up rubbing the cutting tip right off the tool.

The second (lol fourth) attempt I made the relief angles much steeper, and the cutting tip radius much smaller. It did the same thing, ended up completely removing the cutting tip.

Fifth time's the charm? lol.

@Billh50 would you be able to provide some more pictures of what you have in post #9?

 

[MrWhoopee]

Speed was low (due to the size of my machine), very low (200-400rpm?) Thoughts?

Chris, what is the diameter of your fly cutter?
With a high speed cutting tool, 200 rpm would be appropriate for a cutter of approximately 1.50 diameter, at 400 rpm the cutter would need to be under 1 in. diameter. I think you're running too fast.

 

[chris.trotter]

I read something somewhere (lol) that said HSS needs faster speeds (like 1500+rpm). During my geometry tests, I try low and high speeds.

If by diameter you mean, the circle the cutting point turns around, I think it's something like 3-4". Is this something I can look up in Machinery's Handbook? (I have a copy, but have no experience in using it as a tool)