Nathan the Machinist
KnifeMaker / Machinist / Evil Genius
Moderator
Knifemaker / Craftsman / Service Provider
- Joined
- Feb 13, 2007
- Messages
- 17,707
From time to time I'll do runs of custom parts for the people on this forum. Sometimes I'm able to take requests. Earlier in the year some of you asked me if I'd do a run of high quality steel grinder disks. Apparently there is a dearth of decent 9" steel disks. I said I'd be glad to do it when I'm able to and that time has finally come.
The purpose of this thread is to both illustrate the machining process, which a lot of folks find interesting and educational, and also to generate some awareness of the project so people are aware of it when they're finally done. So this thread is part advertizement and part documentary of the machining process.
For an overview, I'm making some high quality 9" (8.875" actually) grinder disks out of alloy steel. They're going to be roughed out, heat treated, machined, welded, re-machined to eliminate runout between the bore and the working surface, broached and balanced. The project is under way now.
I started with a large sheet of 1/2" 4130 chromoly steel and had it delivered to a race shop with a waterjet 1/2 a mile from me. Any Dale Earnhardt fans here? His shop. They roughed it out into disks for me and I drove them down to a local heat treat shop that can handle large loads like this where they were hardened and tempered to HRC 42-44 with a temper at 750 degrees.
So this is what I started with:
A thousand pounds of rough scaly hardened disks.
While I was waiting on them I had gone ahead and made the stubs. These started as 12 foot bars. I cut them in half before attempting to turn them in the lathe so I wouldn't have a dangerous amount sticking from my head stock. This is a video of turning the stubs if you're curious:
[video=youtube_share;FmPPKU_ucS4]http://youtu.be/FmPPKU_ucS4[/video]
Only cut the OD and part it off here. I'm better equipped here to drill it out on a mill so I didn't even attempt that part of it on the lathe. The hole is cut undersized so it can be single point bored to dimension at the same time I cut the face of the disk. Finishing both features in the same operation will prevent inaccuracies such as runout from causing wobble and vibration.
And from there I added some holes for set screws. I don't want to try to drill and thread holes after it is welded to the disk because they would be largely inaccessible.
These holes don't go all the way through to the bore. I don't want to violate the bore with holes or a keyway until after it is finish bored to prevent the possibility of artifacts from an interrupted cut from affecting the accuracy of the bore. The holes are milled with a square bottom and the thread is milled, not tapped, so it can go all the way to the bottom of the hole. That way I'll have a full thread form once I broach the keyway.
The stubs are finished.
Next I mounted one of the prehardend disks in the lathe to turn the back side of it and cut the pocket for the stub
Insert life was very poor. I had the holes roughed by the waterjet because I didn't relish the thought of drilling a lot of holes in hardened steel. I didn't anticipate how hard little bumps left over from the waterjet was going to be on tooling. Add that to some scale and the insert life was awful which made holding the .0005-.001 interference for the press fit impossible. So I put it on a mill to rough the pocket out. While I did that I cleaned up some spots in 120 degree increments to have an accurate surface to chuck on. Then all I had to do on the lathe was clean up the surface that will be the back of the disk and finish bore the pockets to accept the stubs
This worked out pretty well
That doesn't suck.
While I was at it I went ahead and turned the disk around and roughed the other side to so I'd have a nice flat surface to reference against to help me press the stubs in straight.
The purpose of this thread is to both illustrate the machining process, which a lot of folks find interesting and educational, and also to generate some awareness of the project so people are aware of it when they're finally done. So this thread is part advertizement and part documentary of the machining process.
For an overview, I'm making some high quality 9" (8.875" actually) grinder disks out of alloy steel. They're going to be roughed out, heat treated, machined, welded, re-machined to eliminate runout between the bore and the working surface, broached and balanced. The project is under way now.
I started with a large sheet of 1/2" 4130 chromoly steel and had it delivered to a race shop with a waterjet 1/2 a mile from me. Any Dale Earnhardt fans here? His shop. They roughed it out into disks for me and I drove them down to a local heat treat shop that can handle large loads like this where they were hardened and tempered to HRC 42-44 with a temper at 750 degrees.
So this is what I started with:
A thousand pounds of rough scaly hardened disks.
While I was waiting on them I had gone ahead and made the stubs. These started as 12 foot bars. I cut them in half before attempting to turn them in the lathe so I wouldn't have a dangerous amount sticking from my head stock. This is a video of turning the stubs if you're curious:
[video=youtube_share;FmPPKU_ucS4]http://youtu.be/FmPPKU_ucS4[/video]
Only cut the OD and part it off here. I'm better equipped here to drill it out on a mill so I didn't even attempt that part of it on the lathe. The hole is cut undersized so it can be single point bored to dimension at the same time I cut the face of the disk. Finishing both features in the same operation will prevent inaccuracies such as runout from causing wobble and vibration.
And from there I added some holes for set screws. I don't want to try to drill and thread holes after it is welded to the disk because they would be largely inaccessible.
These holes don't go all the way through to the bore. I don't want to violate the bore with holes or a keyway until after it is finish bored to prevent the possibility of artifacts from an interrupted cut from affecting the accuracy of the bore. The holes are milled with a square bottom and the thread is milled, not tapped, so it can go all the way to the bottom of the hole. That way I'll have a full thread form once I broach the keyway.
The stubs are finished.
Next I mounted one of the prehardend disks in the lathe to turn the back side of it and cut the pocket for the stub
Insert life was very poor. I had the holes roughed by the waterjet because I didn't relish the thought of drilling a lot of holes in hardened steel. I didn't anticipate how hard little bumps left over from the waterjet was going to be on tooling. Add that to some scale and the insert life was awful which made holding the .0005-.001 interference for the press fit impossible. So I put it on a mill to rough the pocket out. While I did that I cleaned up some spots in 120 degree increments to have an accurate surface to chuck on. Then all I had to do on the lathe was clean up the surface that will be the back of the disk and finish bore the pockets to accept the stubs
This worked out pretty well
That doesn't suck.
While I was at it I went ahead and turned the disk around and roughed the other side to so I'd have a nice flat surface to reference against to help me press the stubs in straight.
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That sure is some beautiful welding right there. :thumbup: Of course I would not expect anything less from you. 