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Surfacing aluminum head on a model 85 rotary broach

Posted: Fri May 22, 2020 10:07 am
by Raybo
I have a an attachment that bolts to the cutting head and holds one piece of tool steel. Anyone surface aluminum on these machines?

Re: Surfacing aluminum head on a model 85 rotary broach

Posted: Fri May 22, 2020 12:11 pm
by mag2555
The main concern is the feed rate.
The resulting finish from the cutting needs to be so fine as to be reflective so as to not abrade the head gasket fire ring during expansion and contraction .

Re: Surfacing aluminum head on a model 85 rotary broach

Posted: Sat May 23, 2020 8:32 am
by Raybo
mag2555 wrote:
Fri May 22, 2020 12:11 pm
The main concern is the feed rate.
The resulting finish from the cutting needs to be so fine as to be reflective so as to not abrade the head gasket fire ring during expansion and contraction .
I have no way to change feed rate independent of head RPM, I spoke to a tech at Goodson and he said I can convert to PCN or CBN but its a hefty price tag. Id buy another machine before I did that. Just trying to see if this is a possibility. Machine works good for cast iron.

Re: Surfacing aluminum head on a model 85 rotary broach

Posted: Sat May 23, 2020 9:10 am
by Dave Koehler
Concerning that bolt on tool bit.
You will notice that it has a wide cutting edge.
That was to make up for the lack of feed control.
Take small bites. You have been warned.
Make sure the head is clamped real secure. You have been warned
Practice on a junker first.

You can experiment with the cutting angles to get a better cut.
It is better to have a variable feed when doing this.
A variable feed control will change your life.

Re: Surfacing aluminum head on a model 85 rotary broach

Posted: Sat May 23, 2020 6:08 pm
by modok
I would not be excited about it, the old headmaster is not very rigid or accurate.
You could put a variable feed on it easy...but getting it to cut straight and flat may be a hobby in itself.

Re: Surfacing aluminum head on a model 85 rotary broach

Posted: Sat May 23, 2020 7:12 pm
by Dave Koehler
Modok,
Just how worn out was yours?

Re: Surfacing aluminum head on a model 85 rotary broach

Posted: Sat May 23, 2020 11:28 pm
by modok
Van norman 570 upside down rotary broach, had a LOT of wear in the ways, but it still would cut flat enough overall that you could lap the head on a surface plate to improve the surface as desired, without much trouble.
That's not going to be a profitable way to resurface heads, but between you and me, that's a perfectly good way to make a flat surface, for many purposes.

The ol headmaster on the other hand.....was not so much that it was "worn", it was HOW it was worn, would produce a mind bending warpage that was curved cupped AND twisted, had to leave about .003" for grinding flat.
There is a reason that nobody makes em like that.

I've learned a LOT about re-building machines since then, and it would be very challenging to re-scrape that thing, I would not take one if it was free. Cuts and arc :lol: If your making parts shaped like a slice of pizza then it would make sense, but heads are generally rectangular, straightedges are straight.

But can it cut aluminum? sure. Gear it up by changing the pulley, put some kind of inserts for aluminum, slow the feed.....it'll cut aluminum into a lovely twisted cupped arc.