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how to drilling a long hole in a square bar

RE: how to drilling a long hole in a square bar

Custom ground cutter in a mill.

First pass, end mill the slot, then go after it with the custom cutter to get the round shape. Treat it like you're milling t-slots into a table, but with a round profile.



Alternatively, if you absolutely have to use a drill, or can't get a custom cutter... I'd start with a larger block that encompasses the hole size completely, get a decent gun drill, drill the hole, then mill the block to size, opening the hole up.

You don't specify tolerances, quantities, etc, so it's hard to give one answer.
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5

RE: how to drilling a long hole in a square bar

After cutting the long slot (as a rectangle), mount a ball-shaped burr bit in a good tight-fitting clamp and pass it down the slot cutting off the edges of the rectangle into a round.

Can't do it in one pass though.

RE: how to drilling a long hole in a square bar

(OP)
I have to make 2 pieces
Bore Tolerance: +/- 0,5

RE: how to drilling a long hole in a square bar

Just have it gundrilled and open it up with a milling cutter. BTW, there are spherical end mills which may or may not have some tangency interference, you'd have to check it out.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: how to drilling a long hole in a square bar

Is it 1045 cold drawn bar? I think that thing would look like a banana if you mill after drilling. Either way, if it is cold drawn, and you mill the profile, or drill the hole and then mill the surface off, you are going to be locally removing residually-strained material and the freed-up stresses are going to put a bend in it.

RE: how to drilling a long hole in a square bar

If that's supposed to guide something, you'd probably be better off sort of turning it inside out, and making it into something more like a lathe way, with a keystone shaped rib cut from a rectangular bar. Forget the round-ish features; just make every surface flat, so you can mill and grind the bar with big tools, working from the outside. Put all the fussy little weak details on the slider, or whatever you're trying to guide.

Mike Halloran
Pembroke Pines, FL, USA

RE: how to drilling a long hole in a square bar

DVD raises a very good point - stress. Don't forget to rough the part out, stress relieve and then finish. That way you stand a chance of keeping to tolerance.

RE: how to drilling a long hole in a square bar

(OP)
thanks to all for your comments
I found a machining shop that was willing to give it a try. They are going to try to do the hole in a lathe
If this does not work I may be doing a redesign on the guide. I need something that is easy to make
I will comeback when the test has been done

RE: how to drilling a long hole in a square bar

(OP)
The lathe trial did not work

I have changed the design of the guide. I bought a steel tube and made 3 supports (they are needed to bolt the guide to the machine) and the next step is to ground mill the face that is laying on the table (see picture attached)
So far looking good

Will be coming back with the finished guide report

RE: how to drilling a long hole in a square bar

(OP)
I think I used a wrong terminology

Ground mill?

Slab mill

RE: how to drilling a long hole in a square bar

I wonder if you could find someone with the right horizontal mill to get it done the way you first had it designed.

RE: how to drilling a long hole in a square bar

my advice 1. drilling process for a length of 500 could use the gun-drill in the lathe. after drill hole 9, then the milling process to make the groove width 6 and facing up to a thickness of 24.

Herman
http://mymachineinfo.com

RE: how to drilling a long hole in a square bar

(OP)
thanks but, I managed to solve the problem by redesigning the guide like I said on May 21th

RE: how to drilling a long hole in a square bar

Another way would be to use 1" square bar and mill it to size, use a 5mm end mill to rough out the slot, then use a ball nosed slot drill to finish the round section and then finally finish the 6mm part of the slot by opening it out with the 5mm end mill. Several passes would be needed with the ball nose. Finish with a piece of abrasive paper.

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