slot chisel

[Bill Shields]

Whatever you do...take the entire width at once...

[liveaboard]

Good; now that the basic has been established, has anyone got any nice pictures of that sort of chisel, particularly the cutting edge?

[Bill Shields]

Keyseater.com

Google Morrison keyseater for lots of ideas

Mount the cutter on a bar

Guide the bar top and bottom

Feed the work into the cutter.

Trick is to guide the bar stationary while the work moves.

When you see how Morrison does it, you get ideas.

With a horizontal mill that has a tail support for the shaft, the solution is obvious.

[Harold_V]

a broach would still not be the tool for this job I don't think.

Not true. It could easily be broached, but only if the broach was designed for the length of cut.

one job doesn't merit the expense.

Bingo! I totally agree! If you had unlimited funds it might not matter, but folks like us generally find work-arounds that will repalce expensive tooling that is likely to never be used again.

My concern with using a narrow tool and then widening the groove is that tool flex might create a V shaped cut, and I suspect that is why you are recommending a full width chisel.

Assuming you're going to cut in steel, not hardened, I was more concerned about the idea that the tool might rotate away from the desired orientation, not so much about deflection, although that, too, is a concern. If you grind your tool such that it is the proper width, then the only concern is to achieve the proper depth. Rake plays a huge role in how the tool will behave, but the geometry tends to be confusing since the cut is achieved on the end of the tool instead of the top (assuming a tool ground from one piece, not one inserted in a shank). Just think of a parting tool, but with the end of the tool sharing the form of the top.

In this instance you have a reasonably large bore, so you could use a short piece of ½" HSS inserted in a shank @ 90° that fits your largest collet (the larger the diameter, the more rigid would be your setup). In that case, the tool could look exactly like a parting tool, as it would be used in the same orientation. While Bill's comments about supporting the opposite end have merit, you can still achieve success without opposite end support, and that will simplify your setup considerably. Just make the shank robust enough. With a sharp cutting edge and proper geometry, you'll achieve your goal. Remember, each pass will be quite shallow, so cutting pressure isn't all that great, so there shouldn't be much deflection, if any at all. Even then, it will manifest itself in depth, not width, and depth isn't critical.

Make sense?

H

[liveaboard]

Yes, thanks.
I'm planning to have some sort of positive lock against rotation of the tool, I don't yet know how. If it's just set into the tool holder bearing cone it will rotate all over the place.
Probably a strip of steel welded to the push shank, that will reach out a little and bolt to the mill slider somewhere next to the tool holder.

[Bill Shields]

You do have horizontal capabilities with a tailstock for the tool arbor...correct?

[liveaboard]

That is correct.

[Bill Shields]

Think about mounting the chisel horizontal on a bar held in the spindle and guided by the cutter support.

This gives you a solid cutting setup.

[wally318]

This type of job is best suited to a slotting head driven off of the horizontal spindle.
There may have even been a slotting head that was made for your Ruhla mill.
Deckel/aciera/schaublin and all the other copies had a slotting head as an attachment.
They had an adjustable stroke to 80mm and speed was controlled by rpm of horz. spindle.
They had slotting tools with different profiles. Google slotting tools. Specifically Bridgeport
slotting tools and you will see the different shapes.
I brought in a Parkson slotting head from the UK to Canada and adapted it to my Rockwell
horz/vert. mill as part of the rebuild. Will be doing the first cuts in the next few weeks.

[liveaboard]

You're right, there is (was) a Ruhla slotting head accessory.
If anyone has one, I've never seen it.
There are many cool things in the literature; a tilting table (those are fairly common), a powered rotary table (little drive shaft fits in somewhere) a high speed boring head, etc.
Most milling machine accessories seem to get lost if they're not attached to the machine. I have a rare one in that mine still has the original horizontal brace bearing. Most don't even have that.

I subscribe to a German forum where a few people have the same mill, but all in all I don't think there are many still operational. The serial numbers are 3 digits, I think there were only around 600 made in total.
The later versions had even less reliable electrical systems (DC variable speed drive of the 70's) and few were saved from the scrap heap.

I even have an ebay alert for Ruhla, and in 3 years I've never seen a single accessory for my mill up for sale there.
One day, I might build a slotting head.

[Rich_Carlstedt]

I need to make a 12mm wide slot on the inside of a mild steel collar with a 40mm bore.
..........................
The slot is a bit of a wide one; should I make a chisel the full width of the slot, or use a narrow one and work the slot wider a bit at a time?
If the chisel is full width, should it be made as close to 12mm as possible, or intentionally undersize?...............

First, Listen to what Mauro said in post #3
A half inch wide homemade broach takes a lot of power to make the cut so a smaller broach can be the answer like 1/4
The problem with a smaller broach is size control, so the 1/2" width will be more difficult AND a 2" deep slot is not any easier. .
So my addded step to Mauro's is to first drill the corners with a small drill like 3/32's or 1/8" ( See pic #1)
Do it on the corner centers (!) which will help immensely with clean out.. Use a jig for guidance in starting both holes !
The holes actually help by eliminating stress on the key cutout

Keyway clean out.jpg (23.16 KiB) Viewed 546 times

Making a broach is easy with old used or broken taps.. Just the right harness for shaping.

P7170215.JPG (77.82 KiB) Viewed 546 times

Rich

[wally318]

If you're going to use the broach method.
Then machine a broach bushing. 1/2 inch wide
use a 1/4 " broach and do 2 passes of 2 cuts for each
1/4" of width. A broach is certainly capable of 2" deep cut
but your mill is not! Save your quill and feed components
and do it proper on a hydraulic press. The simple
jack kind is fine. On a 2 or 4 ton arbor press with an
18 inch handle you will find that you will need a 4 ft long
cheater bar put onto the handle for enough force, if you are
going through steel.
What is your quill drive compared to that? And with that method
its not as smooth as on any type of hydraulic press so chance
you could snap the broach-being HSS.