Atlas MFB Arbor Keyway

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Tonaven

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I just acquired a vintage horizontal mill, which came with no tooling other than a single 1/8” wide cutter. I did get a 1” arbor for it along with a set of spacers. The arbor has a 1/4” keyway in it, the cutter has the same sized keyway in it, but the spacers do not have a keyway in them. So there is a problem that I cannot put a key in the keyway to hold the cutter in place, as the spacers have no keyway in them.


I see three possible solutions:

1. Don’t bother with a key, just tighten up the spacers hard and hope they will prevent the cutter from spinning.

2. Use a piece of key that is relieved part way along its length on either end, such that the relieved sections would fit under the spacers on each side of the cutter, while the remaining center part of the key will support the cutter.

3. Broach a keyway in two of the spacers. The spacers are only 3/16 thick however so if I put a .125” deep keyway into them there is not much material left. A variation on this is I could make some thicker spacers and broach them. Plus I have no way at present to broach.

I welcome any insight or suggestions on how I should proceed.
 

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The slitting saw might work without a key, but anything bigger will have to be keyed. I'd opt for keyway cut spacers. Bought as singles, broaches aren't too expensive, especially used. Since you'd be pairing it with a machine, it might not be a bad idea to have one. Of course, you need an arbor press to go with it. Hmm, maybe McMaster sells keyed spacers...
 
It was typical to use slitting cutters without keys in lighter duty machines taking light cuts. Keyed spacers are easily availabe, if the ones you have are hardened, broaching keyways in them is not a viable option.
 
Choice 1 is out. Sooner or later the thing will slip and screw up both the arbor and the work piece. Choices 2 or 3 might work but are unnecessary. Broach sets may be expensive but a single size is not. Buy one and key the spacers that you have and be done with it.
 
Thank you all.

I checked on McMaster and they do indeed sell keyed spacers! Good tip there. I will just buy two, one to fit either side of the cutter, should be enough for now.

McMaster also sells keyway broaches, bushings etc, but that would be a bit more expensive, so I will wait on that for now.

Thanks again.
 
KBC Tools in Delta also sells them, that’s where I got mine. Don’t know how their shipping compares to McMaster but it’s another option.
 
If you live in Canada try to support Canadian retailers, else we lose them. Also check Kijiji and FB Marketplace.

For this specific case I would grind an appropriate HSS tool, mount it on the cross slide of your lathe and broach the keyway using the carriage.

Or in the mill:
 
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