What would a real machinist do?

Been doing this stuff for a living for about 30 years.

Assume only 1 piece, not to mess it up.

REAL home machinist way:

(if you don't have a lot of tools)

Clamp practice part in v-block.

Locate v-block securely against a stop. (or in a vise)

Mill 1 slot off center.

Rotate v-block 180 degrees.

Mill another slot.

Measure spacing and adjust table position.

Mill good part as above.

(if you have a lot of tools)

Clamp part in v-block on mill.

Edge find for center.

Cut a practice piece anyway.

Adjust table position for correct spacing.

REAL at work machinist:

Clamp part in machine.

Probe and program slots.

Run program.

All depends on the machines and tooling on hand.

Best Regards Tom.

Jumping in anyway, I'd hold it in a 5C collet block. 1-1/8 is the largest size and the work won't pass through. Mine steps down smaller

1-3/4" in.

Otherwise it's an excuse for a rotary table for your milling machine.

Perhaps you could leave it long, turn fine lines at the inside and outside diameter of the slots, and mill to them by eye. That would avoid unclamping and rotating it.

js

Edit that to a shallow circular groove in the end, so you can bore its ID and OD to measured size and see better when the milled slot's width approaches tangency.

jsw

If I were a real machinist, I would clamp the piece horizontally in a milling vice using v blocks on the stationary jaw protruding at least

3/8 off one side, then put a .125 thick slotting saw in the mill and lower the quill until the lower edge/side of the saw touches the top of the 1.125 round. I would zero the quills DRO and move the saw so that its top edge now touches the bottom of the round. I would half the DRO reading and move the quill to that position an re-zero the DRO. I then would zero my x axis so the saw blade just touches the round at approximately y axis 0. Now I would move the saw up 0.260 and mill the slot until the x axis reads -.250 , then return and move the quill to

-0.260 and again mill the slot to x -.250. This places the center of the slots apart .520 If you desire the inner edge of the slots to be .520 apart, then you have to add .0625 to each quill move.

cheers T.Alan

I would have hung the business end out the left side of a kurt vise and then used a 1/8 wide x 3 diameter wheel cutter mouted on a stub arbor.

For higher production, I might use a pair of wheel cutters instead of just one.

Several people have already responded with a lot of good tips. I think it also might be worthwhile to understand what went wrong with your first attempt. If I remember you have a chinese minimill. I have one too and I know to get good results you have to keep its weaknesses in mind. For example, if you do not partially lock the moving axis it will have a lot of wobble. Even so, this mill is not very stiff, and the force of the cutter entering the angled edge of the bar might be enougth to shift the cutting tool. Another thing to watch out for (that I presume you know) is, if you have the inch version, one turn of the crank is 0.063", so it is easy to lose track of your position. I installed some of those cheap, battery-powered linear encoders after I was bit by this a couple of times.

If I am cutting anything important on the minimill, I always leave 0.020" of extra material, make a measurement, and then cut the remainder. Granted this is difficult to do with an 1/8" slot when using an endmill. So, as others have suggested, I would use a slitting saw or wheel cutter.

If you are "milling" clamp the piece in the mill. Pick up one side, set cutter center for first slot and mill. Move cutter to second slot position and mill. Use edge finder to "pick up" side of work and table feed screw dials for movement.

Do they have enough torque at a low enough speed for a 2" slotting cutter?

jsw

If you cut too deeply with a long thin endmill the cutting force deflects it sideways. IIRC when I tried a similar cut I had to restrict depth of cut per pass to around 0.025" and feed slowly. I didn't have a slitting saw the right width and diameter.

2-1/2" saws push the limits of my 700 Lb, 3/4HP Clausing mill.

jsw

I have no clue what a real machinist would do, but I might do it by chucking it up in the manual rotary table I spent several days mounting a chuck on several months ago, and do it all on the manual mill.

I think these mills have more low speed torque than the Sherline mill (which that cutter you linked to was sold for). I have to admit I do not have first hand experience using a real slitting saw. I have used an abrasive cutter at high speeds, and I have a used a wood/plastic dremel saw on aluminum with small cutting depths.

There are some responses to the attached thread from folks saying they even use 3" cutters with very shallow cuts.

I'm not a real machinist.

Assuming that I knew how to use and edge finder to find the center of a drilled hole:

I'd get the part clamped into my milling vise such that the cylinder was as vertical as I could get it. Then I'd use my hypothetical center- finding skills to locate the center. Then I'd spin up 0.26 inches and over half the length of the slot (you didn't say), machine my slot (in bits -- 1/4" deep is a lot for a 1/8" bit, not to mention my wobbly machine).

Then I'd spin down 0.52 inches and make the other slot.

But I don't have an edge finder that finds the center of holes, nor would I know how to use one, so I'd use my plain ol' edge finder to find the edges of the cylinder. This is a tedious process because you have to repeat a few times so that in the end you're hitting the top of the arc

-- but I've done it, and it seems to work.

Once the four sides are found, I'd spin over to center, then I'd proceed as above.

Or, since you didn't mention tolerances, I'd just eyeball it, whack out any two slots between 0.1" and 0.2", and say it matches the print.

[...]

I did a version of this. I made a slight dimple in the center of the face by a spotting drill in my lathe. In retrospect this is not the best way as the dimple is quite shallow and the centre finder which I used subsequently does not have a well defined center to sit in. In future I will try my optical punch and line it up on the concentric rings from facing off.

Anyway, got the center, moved off 0.3225" and milled the first slot in

0.020" passes, 0.25" deep as per dial indicator on the Z-axis. Using another indicator I walked back 0.645" (the other side of center) and milled the second slot. That's when I had a hiccup forgetting to lock the table and paid for it. This contributed to the asymmetry. The other component is the centre finding.

I like the idea of the slitting saw, though. I might even get one.

Michael Koblic, Campbell River, BC

I am not a real machinist (nobody pays me regularly for my work), but using my tools, I would use a horizontal mill and two 0.125" thick slitting saws or milling cutters, and a spacer whose length is proper to hold the two cutters the right spacing. You don't say whether the spacing is from center to center of the slots, or distance between inside edges of the two cuts, or what, so I don't specify the length of the spacer.

Then the trick is moving one cutter the right distance off the fixed jaw of the vise. (I would likely use an adjustable parallel set up to produce the right offset with a piece of paper thickness calculated in for the edge of the cutter to just barely kiss to protect the adjustable parallel.

Then place the workpiece against the fixed jaw, and a V-block between the moving jaw and the workpiece to hold it firmly in position.

The index head trick works too, if you have only one 0.125" cutter.

Enjoy, DoN.

On a vertical mill, an easy way to do this is with a height gage..,,set a zero on the part, then raise the knee to bring the cutter to the same height and set the dial on the knee crank to zero...finally, crank the knee up by the desired amount.

Basically the same can be done with a planer gage, by setting it to the underside of the part, but you also need to pay close attention to backlash.

Here is the finished part:

and here is a different version of the same thing:

BTW not having a vise large enough to accommodate a v-block as well as the part I found that a piece of leather cut off an old belt against the moving jaw works just nicely!

Michael Koblic, Campbell River, BC

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