slot chisel

[liveaboard]

I appreciate you guys taking the time to answer; but as I said, I will not be using a broach, but a chisel to scrape away a small shaving at a time.
The grove is long and wide, and I will only be making one part. That does not merit the cost of a dedicated tool.

And that idea about drilling long small diameter holes first; all I can say is you have a far higher opinion of drill bits than I do.
My experience is that such drill holes are unlikely to be straight, and the odds of breaking off a bit deep inside the work is high.
Further, I see no advantage to having the holes there even if I would succeed in creating them.

I made an error earlier, the key is not 50mm long but 80. With the additional length to fix the next part to, the collar I made for it (yesterday) is 95mm long, nearly 4"

[Bill Shields]

maybe the chisel can be a hss lathe bit stock of the correct width, clamped in a cross drilled hole in a piece of bar stock.

i have done similar long ago...not very pretty, but it worked.....

need picture to envision?

[liveaboard]

The tool is already under construction; I don't have much hss except drill bits, so the first attempt is a 13mm cobalt drill bit shank set into a 32mm mild steel rod with a 10mm clamp bolt.
It will be secured against rotating by a short steel arm bolted to the mill head mount (I removed the vertical milling head for this).

Of course, there will be pictures.

[Bill Shields]

[Harold_V]

Be advised that drill bit shanks are not hardened. That's by design. If you use the shank near the flutes, that may not be true.
For those who don't know, drill bits are induction hardened, which is a fast and highly controlled operation. By leaving the shanks soft, they are gripped better with conventional drill chucks, which indent the shank slightly, with the idea in mind of preventing slipping.

The shank of an old end mill would be a better choice as they are fully hardened.

H

[liveaboard]

I made the chisel and it's working ok; the cutting end is just where the flutes ended into the shank.

The (nearly) full width first attempt required too much force to push through, even taking ultra-shallow cuts. The safety clutch on the feed wouldn't let me do it once the whole face was engaged (the first couple of passes worked as only the outer corners were cutting into the walls of the bore).

After grinding the chisel down to 6mm wide it's cutting well, making nice curly ribbon chips. It's time consuming and I got about halfway through before the heat relay on the feed motor told me it was quitting time. I have one 6mm groove at full depth and the cut looks good.

I'm taking 0.2mm deep cuts, still I have to take 2 or 3 passes at each setting due to deflection.

I'm using the fast traverse button to speed things up, so the motor load is a bit heavy.

[ctwo]

I would mount the piece in my lathe, lock the spindle, and use a boring bar to slot.

[Harold_V]

I'm taking 0.2mm deep cuts, still I have to take 2 or 3 passes at each setting due to deflection.

That, coupled with the comment about too much force leads me to suggest that your geometry isn't quite right. With more positive rake, the cut would be with much less effort and would likely not deflect as much, if at all.

I suggest you examine the cutting tool for signs of contact where it isn't desired. You'd be looking for a shiny spot where there shouldn't be one. If there's any doubt about unwanted contact, coat the entire cutting end with a magic marker before taking a cut. Where it wears away will show the area in contact.

H

[liveaboard]

The job was completed yesterday; it came out ok but could have been better.
An error in the tool cut into the top edge of the slot as I made the last few passes.
The cutter has plenty of rake; the situation improved after a slight sharpening, also tightening the clamp screws against the cutter bar.
After that I only needed to take an extra pass after every 2 increases in depth.

Dimensionally, the slot is quite good. It would have been easier if I'd made the key first, so I could use it as a measuring tool. It was difficult to fit my calipers in there while everything was mounted.

collar slot 1.jpg (81.13 KiB) Viewed 823 times

slotting setup2.jpg (111.38 KiB) Viewed 823 times

slotting setup1.jpg (106.56 KiB) Viewed 823 times

collar slot 2.jpg (72.55 KiB) Viewed 823 times

[Harold_V]

I figured there had to be some issue with the tool.

Good to see you got it resolved. Quite satisfying when a guy can solve a puzzle like this, and you certainly did. Well done!

H

[liveaboard]

Thanks; of course the truth will be known only when the part is completed (I will press and weld a small gear into one end) and then pressed onto the shaft.
If everything is right, the press force will be a few tons.

[Harold_V]

Hmmm. Welding on the piece is likely to cause some distortion. It might have been wise to do the welding before sizing the bore and creating the keyway. Would that have been possible?

H