Advice Please: Finishing Tapered Thru Hole After Machining to 8 Ra

NodecoMachine · Mar 9, 2017

I have a dozen or so "Dies" coming up that need to be finished post machining. They are made of 4140 HT and will be coming off the machine with somewhere around a 32 Ra. I'm just looking for advice on how to finish these holes economically. Last time these parts came thru, I spent probably an hour per part :cryin:

. Other info would be the holes are 1-1/4" long and have a 6 degree taper included approx 15/16" of the way thru the hole. Also the holes will range from 1/4" to 1-1/4" thru. I ended up using flapper wheels with grit ranging from 120-400 before finishing with emery in the last batch but the thru holes were much larger. I think around 4".

Thanks in advance.
Scott

P.S. I also have another batch of dies coming up that are much longer (5-1/2") and need 18 Ra finish with size range of 3/4" to 3" thru.

i_r_machinist · Mar 9, 2017

I don't know what machining process is "banking" out the holes, but if it is on any type of modern equipment, you should be getting at least a 16rms to start with. Go chew some ass.
have fun
i_r_

implmex · Mar 9, 2017

Hi Scott:
Your basic problem is that the machining process you're using is really not the most favourable one for this level of surface finish and this part geometry.
Yes, with luck you can occasionally hit it, but it only takes a single chip or a tiny crater in the tool tip and you're hooped on that part.
Your material doesn't help (unless it's above 45 RC).

These parts really should be either wire EDM cut or cylindrical ground, not finish turned.
Yes you can hard turn the shorter, bigger diameter ones to these finishes in a good stout lathe with the proper CBN or ceramic tooling, but as I commented above, they need to be HARD to get the finishes hard turning is capable of.
Your long aspect ratio and small diameters don't help: that's when wire EDM can be a Godsend.

So if you've already taken them on and can't farm them out, you're likely going to be stuck hand polishing them all.
The long skinny ones will be a real bear to finish, but I can't see a magic solution...sadly you're probably going to have to bite the bitter pill.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

NodecoMachine · Mar 9, 2017

i_r_machinist said:
I don't know what machining process is "banking" out the holes, but if it is on any type of modern equipment, you should be getting at least a 16rms to start with. Go chew some ass.
have fun
i_r_

I do not believe I mentioned "banking" out the holes and it seems this machine is getting a bit worn out because 32 about as good as it'll get. When I try to get a better finish, the parts come out with a bit of a wavyness. In any case, maybe a series of flex hones would help with the small ones?

NodecoMachine · Mar 9, 2017

implmex said:
Hi Scott:
Your basic problem is that the machining process you're using is really not the most favourable one for this level of surface finish and this part geometry.
Yes, with luck you can occasionally hit it, but it only takes a single chip or a tiny crater in the tool tip and you're hooped on that part.
Your material doesn't help (unless it's above 45 RC).

These parts really should be either wire EDM cut or cylindrical ground, not finish turned.
Yes you can hard turn the shorter, bigger diameter ones to these finishes in a good stout lathe with the proper CBN or ceramic tooling, but as I commented above, they need to be HARD to get the finishes hard turning is capable of.
Your long aspect ratio and small diameters don't help: that's when wire EDM can be a Godsend.

So if you've already taken them on and can't farm them out, you're likely going to be stuck hand polishing them all.
The long skinny ones will be a real bear to finish, but I can't see a magic solution...sadly you're probably going to have to bite the bitter pill.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

I agree an EDM or cylindrical grinder would help tremendously with these parts but I forgot to mention in the OP that the holes have a 1/8" radius on both sides which, if I am not mistaken, rules out a wire EDM and manual cylindrical grinder. In the future, if we found a shop with CNC cylindrical grinder, would they be able to grind those radii?

implmex · Mar 9, 2017

Hi again Scott:
Yes a CNC cylindrical grinder could probably do it, but since those features are readily accessible, they could be put on using a separate machine.
Not super efficient, but workable.
I like wire EDM for long skinny internal cones just because it's just so easy to make them super nice and the length to diameter ratio almost doesn't matter so long as the part will fit between the wire guides and the taper isn't extreme.
That's worth a lot, and may justify the PITA of setting up the lathe to do the radii as a separate operation.
Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

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