I set my bridgeport up to cut a thin slot in a piece of steel. So far I
have only broken bits.
I dont know much about hardness but the material I am using has a black
coating. Not sure what that is. But I started off with a 1/8" endmill
taking very light cut at a very slow speed. I am having no luck.
Additionally, I need my slot to be deeper than the endmill itself.

What I am doing is setting up a 2 brackets to hold a 1/8" x 1.25" x 12"
long cutting bar. I am sure there has to be an easier way but it might
take more pieces than cutting from one.

Any suggestions?
Thanks

gtslabs wrote:

I set my bridgeport up to cut a thin slot in a piece of steel. So far I
have only broken bits.
I dont know much about hardness but the material I am using has a black
coating. Not sure what that is. But I started off with a 1/8" endmill
taking very light cut at a very slow speed. I am having no luck.
Additionally, I need my slot to be deeper than the endmill itself.

What I am doing is setting up a 2 brackets to hold a 1/8" x 1.25" x 12"
long cutting bar. I am sure there has to be an easier way but it might
take more pieces than cutting from one.

Any suggestions?
Thanks


If the slots are open ended, couldn't you just use a slitting saw?

And if they're not, maybe you could make them that way anyway and silver
solder some 1/8" thick stops at the ends?

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

I assume you mean a slow feed rate, but not a slow cutter rotational
rate--- My amatuer calculations say that end mill should be run at
3200 rpm if stock is mild steel and mill is HSS. I read somewhere that
the main cause of small drill bit breakage is running them too slow. I
suppose the same thing would go for your end mill.

As far as hardness of your material goes, simply use a good file and
compare the unknown material's "fileability" with known hard or soft
stuff. If your mystery metal is a lot harder to cut than some mild
steel, toss it and get some known material.

But:

I would simply make the part from 3 pieces and bolt them together. The
center piece would be the 1/8" thick material that would space out the
outer sides.
Hope this makes sense,
Pete Stanaitis
--------------------------

gtslabs wrote:

I set my bridgeport up to cut a thin slot in a piece of steel. So far I
have only broken bits.
I dont know much about hardness but the material I am using has a black
coating. Not sure what that is. But I started off with a 1/8" endmill
taking very light cut at a very slow speed. I am having no luck.
Additionally, I need my slot to be deeper than the endmill itself.

What I am doing is setting up a 2 brackets to hold a 1/8" x 1.25" x 12"
long cutting bar. I am sure there has to be an easier way but it might
take more pieces than cutting from one.

Any suggestions?
Thanks

You certainly can mill a slot that width to that depth, but it is going
to take extended length cutters. Long cutters chatter, especially when
cutting around their entire perimeter in a slot. Carbide cutters work
better when dealing with difficult length to diameter ratios because
they are stiffer. You just have to be careful with carbide not to
chatter them or they loose their edge.

I might take .010" at a pass, at about 5 IPM and 2500 RPM, keeping the
slot clear of chips with air or flood coolant. If you make your cut,
then make it again shifted over a few thou in Y both ways, you will
keep the cutter from contacting the side walls as you get further down,
to avoid chatter.

You can cut hard steel this way, so long at it isn't full hard. Crappy
steel, with hard inclusions (chrome chips from the bumper it was made
from, ha!) is where I get into trouble.

I would expect it to take a while to do this, and I wouldn't be
surprised to go through a cutter or two.

According to gtslabs :
I set my bridgeport up to cut a thin slot in a piece of steel. So far I
have only broken bits.
I dont know much about hardness but the material I am using has a black
coating. Not sure what that is. But I started off with a 1/8" endmill
taking very light cut at a very slow speed. I am having no luck.
Additionally, I need my slot to be deeper than the endmill itself.

That is a serious problem, and takes *lots* of patience, and
lots of coolant or air blast to keep the chips cleared out -- *if* you
insist in doing it with an end mill.

What I would use for the task is my old horizontal spindle
milling machine, with a conventional milling cutter (wheel sort of like
a saw blade) to do the cutting. The smallest ones which fit my machine
are 3" diameter, with the spacers on the arbor being about 1-1/2"
diameter, so those would not reach to the bottom of your cut (barely
3/4" -- so the spacers would drag on the workpiece before you reached
the full depth), *but* there are larger cutters. I have a couple which
are 6" diameter. The ones which you really want for this are the
staggered-tooth ones, one tooth cuts the center and one side, the other
cuts the center and the other side. And, they are available in various
thicknesses.

What they do not do well is produce neat ends of the cuts -- it
will curve up to the surface at either end. However, if your slot needs
to go from one end to the other of the workpiece, it will work quite
well.

With your Bridgeport, you have a choice of a horizontal adaptor
(a right-angle head, an arbor, and a clamp on the dovetails of the ram),
or a stub arbor. The first choice would be the better in terms of
rigidity -- *if* it can handle a cutter over 4" in diameter.

What I am doing is setting up a 2 brackets to hold a 1/8" x 1.25" x 12"
long cutting bar. I am sure there has to be an easier way but it might
take more pieces than cutting from one.

It sounds as though the slots go to the end of the brackets, in
which case the conventional milling cutter should work quite well.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

gtslabs wrote:
I set my bridgeport up to cut a thin slot in a piece of steel. So far I
have only broken bits.
I dont know much about hardness but the material I am using has a black
coating. Not sure what that is. But I started off with a 1/8" endmill
taking very light cut at a very slow speed. I am having no luck.
Additionally, I need my slot to be deeper than the endmill itself.

What I am doing is setting up a 2 brackets to hold a 1/8" x 1.25" x 12"
long cutting bar. I am sure there has to be an easier way but it might
take more pieces than cutting from one.

Any suggestions?
Thanks



Can the holes be pre-drilled slightly smaller than the desired dimension, then
milled to spec? Can the part be flipped over accurately to mill the other side?
Good luck on the project.

On 28 Jan 2006 11:37:22 -0800, "gtslabs" wrote:

I set my bridgeport up to cut a thin slot in a piece of steel. So far I
have only broken bits.
I dont know much about hardness but the material I am using has a black
coating. Not sure what that is. But I started off with a 1/8" endmill
taking very light cut at a very slow speed. I am having no luck.
Additionally, I need my slot to be deeper than the endmill itself.

What I am doing is setting up a 2 brackets to hold a 1/8" x 1.25" x 12"
long cutting bar. I am sure there has to be an easier way but it might
take more pieces than cutting from one.

Any suggestions?
Thanks

Use a horizontal mill. Or a plunge EDM

Gunner

"Deep in her heart, every moslem woman yearns to show us her tits"
John Griffin