Need ideas to mill a radius botom pocket, no cnc.....Help please

k2steve · Apr 26, 2020

I will try to attach a pic of the part. I need to duplicate this mount for a new reshaped clamp. the part is only roughed out but square right now, thought I'd do the part I don't know how first while I can hold it easily.
I cannot figure out a way to do the bottom of the pocket. It is 1" wide, 5/8" radius at the bottom and square to the sides.
Is there a way of doing this, I never learned CNC nor have a machine to play with. just conventional machines and tooling. Thanks for looking, hope there is a way to do this.....Thanks Steve

implmex · Apr 26, 2020

Hi k2steve:
This will be a helluva part to try to mill on a conventional machine; in fact it is an impossible challenge even on a CNC machine because you have to have a long skinny cutter sticking out a mile in order to cut that shape.

If it was my part to make I'd make an electrode and burn it on the sinker EDM but that advice is useless to you.

So my next question is: do you have welding or brazing equipment in your shop?
If so you can make it out of pieces and braze or silver solder them together (or weld them, of course).
Once you've deconstructed it into 2 pieces it will be easier to mill, but it's still not a simple project to make nicely.

Once they're together you can cut all the other features from what is now a single piece with the impossible feature already made.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Terry Keeley · Apr 26, 2020

Thinking out loud here.

Rough the bulk of it out square.

To do the bottom radius could it be mounted to a rotary table on it's side then mount the rotab vertically and using a long cutter end mill the bottom?

The part would be like a pendulum, would that work?

gustafson · Apr 26, 2020

Without CNC you buy tools

big radius cutter, whatever it takes

If it is soft you can grind tools

Limy Sami · Apr 27, 2020

It COULD????????? be done using in effect a boring bar running in the clevis holes with a small HSS cutter at 908 to the bar and taking say 0.010'' cuts at a time by stopping the spindle and advancing the cutter.

But what a ball ache :eek:

plunger · Apr 27, 2020

I may not understand what you are asking but could you not mount it between centers on a lathe with the part bolted to the carriage and use a between centers boring bar with a form radius ground in one end and then either turn the form tool around for the second shoulder or turn the workpart around.

eKretz · Apr 27, 2020

Several ways to do it. As Limy so succinctly alluded, none of them super easy on manual equipment. The way I'd go about it if it had to be one piece and true to form would be to use a rotary table and a vertical mill. Rough the cavity first as close as you can in a vise, then swap to the rotary table. Mount the base of the part against an angle plate at the correct distance from center of the rotary table and use a stiff boring bar to hold a piece of HSS ground as a broaching cutter. Lock the spindle and use the rotary table feed to run the cutter around the radius, infeed a little per pass to get to finish, move the table up/down to complete the radius. Start at the top and feed the cutter in .010" per swipe with the mill table to do the flat sides.

k2steve · Apr 27, 2020

Hello all, thank you for all the responses, tomorrow I will set-up a piece of wood on the rotary table and see what kind of result I get. Like Terry said, set the part on its side with a angle plate on the rotary table with a right angle head on the spindle. This will be new to me, I have never used the right angle head before. I bought it about two years ago so it is time to put it to use...…...Thank you …...Steve

crossthread · Apr 27, 2020

There are not enough dimensions given to support my idea but would it be possible to machine it on a horizontal mill with a 1" wide cutter" If the knurled sides are low enough you could plunge down into the center section.

Terry Keeley · Apr 27, 2020

k2steve said:
Hello all, thank you for all the responses, tomorrow I will set-up a piece of wood on the rotary table and see what kind of result I get. Like Terry said, set the part on its side with a angle plate on the rotary table with a right angle head on the spindle. This will be new to me, I have never used the right angle head before. I bought it about two years ago so it is time to put it to use...…...Thank you …...Steve

That or mount the rotary table vertical...

implmex · Apr 27, 2020

Good morning All:
If the bottom of the pocket is concentric with the bores, you cannot swing it out with a cutter except by Limy Sami's or plunger's methods where the shank of the tool goes through one or both of the bores and the cutter itself is introduced after the shank goes through the holes.
Bringing the pocket out to diameter involves advancing the cutter to increase the radius incrementally until you've protruded the cutter tip out enough to get to your final 5/8" radius, and it's those advances that are a big problem because you have to swing it out maybe 0.001" per pass, not 0.010" per pass and after every advance you have to re adjust the cutter swing radius to make it 0.001" bigger.
Once you've opened out to final diameter you can traverse across the length of the pocket while the cutter is spinning, but the shank of the cutter must remain concentric to the bores at all times if the pocket floor is concentric to the bores and it sure looks that way to me.
So a rotary table won't help you here unless you use it with a little ball cutter sticking out a long way to rough out as much as you can, recognizing you will still need other operations to pick out the corners.

Looking at the photo, I'm guessing the bores are about 1/2" diameter, and the pocket radius is 5/8" per the OP, so the final stickout of the cutter tip is 0.375" from the surface of a 1/2" diameter bar and you have to get there in 0.001" increments after you've roughed out the bore as much as you can.
Conceivably, you could drop an 1 1/4" diameter ball cutter down between the ears of the part while it's standing up in the mill vise (assuming you have 1 1/4" between the ears), and use that cleared area to advance the cutter while the boring bar is stopped, so you don't have to scrape it out in those 0.001" increments, but now you need a 1 1/4" ball cutter.

If you had a CNC mill you could mill everything you can with a 1/4" ball cutter and then just pick out the corners of the pocket with the boring bar through the clevis holes, but it's sooo much easier to just bore the pocket from one side, turn up a round slug of the correct diameter and width to form the ear you cut away while boring the pocket and then silver braze or weld in the round slug to rebuild the second ear, especially if you don't have a CNC mill.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

eKretz · Apr 27, 2020

Yes you can. Using the rotary table method I described. That would basically be rotary shaping. As long as the arc doesn't equal or exceed 90° it's possible. Even then it's possible, just more of a pain. It is not possible with a milling cutter and rotary table, the geometry isn't correct. The boring bar way would work too but it would be a very large PITA also. Could also use a back spotfacing tool with the removable head, cut a cavity large enough to get it in with a ball mill then use that spotfacer to finish the corners and faces from both sides.

gregormarwick · Apr 27, 2020

eKretz said:
Several ways to do it. As Limy so succinctly alluded, none of them super easy on manual equipment. The way I'd go about it if it had to be one piece and true to form would be to use a rotary table and a vertical mill. Rough the cavity first as close as you can in a vise, then swap to the rotary table. Mount the base of the part against an angle plate at the correct distance from center of the rotary table and use a stiff boring bar to hold a piece of HSS ground as a broaching cutter. Lock the spindle and use the rotary table feed to run the cutter around the radius, infeed a little per pass to get to finish, move the table up/down to complete the radius. Start at the top and feed the cutter in .010" per swipe with the mill table to do the flat sides.

That's a nice method, but it would be a slow, slow process, probably slower even than line boring through the holes as suggested by Sami.

Bill D · Apr 27, 2020

Can you simply cut a larger radius and do it on a horizontal mill? It is not clear if the bottom pocket is just for clearance or if something mates to it.
If it has to be mated then a line boring, camshaft type tool will have to be used. Any evidence how it was made?
Bill D

implmex · Apr 27, 2020

Hi eKretz:
At the risk of seeming contrary here, how do you propose to get the nearly sharp corners in the pocket using the rotary table?
If the OP can tolerate radii in the corners, yes you could swing it out with a rotary table and a ball cutter, but if he cannot tolerate at least a 1/8" corner radius at each end of that pocket, the rotary table and a ball end mill will not get all the geometry.
This presumes the axis of the cutter is orthogonal to the axis of the pocket (as it would be if you surface milled it on a CNC)

As soon as you make the axis of any spinning cutter parallel with the axis of the pocket you MUST make them concentric as well to get to the bottom of the pocket, and that means a tee slot cutter of maximum 1 1/4" diameter with a zero diameter shank unless you poke the shank through the bores before you insert the cutter.
As soon as you do that, you may not just stick the cutter out to the correct final diameter and turn on the mill...you'll break the cutter off as soon as it slams into the unmilled pocket.

So you would need to nibble it out bit by bit, growing the diameter by advancing the cutter a tiny bit each time so you can spin it and take a chip without snapping it off.

I do understand with the method you are describing that you never spin the cutter; you are using it like a shaper cutter and traversing from one pocket wall to the other...advancing the mill table to bring the cutter tip successively toward the surface you intend to machine as you swing out the arc using the rotary.
However, what your method neglects is what happens at the beginning of the stroke as the cutter needs to be forced into the workpiece and what happens at the end of the stroke as the cutter piles the chip into the bottom corner of the pocket.
If you have ever shaped a blind keyway on the lathe, you will recognize the problem: unless you've machined a relief groove or drilled a relief hole at the blind end of the keyway...with every successive stroke, the chip prevents you from getting as close to the bottom as you did with the prior stroke, and if you try to force it you eventually break the cutter.

So in theory, your approach can be made to broach out the OP's desired shape, but in practice, it sadly cannot, and when finishing the ends of the pockets (the inside faces of the ears), you cannot use a cutter other than a boring bar, with inserted tip run concentric to the bores and taking the whole of the face width in one pass.
You can sneak in with the smallest shank, largest diameter tee slot cutter you can rustle up to get some of it, but ultimately, you need a boring bar to catch the last bit of the inside corners of the pocket, and you NEED to poke the bar through the clevis bores.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

eKretz · Apr 27, 2020

gregormarwick said:
That's a nice method, but it would be a slow, slow process, probably slower even than line boring through the holes as suggested by Sami.

Having done the bore through a tiny hole method plenty of times...I don't think so. That through hole looks to be at best 1/2". That means probably a 1/8" piece of HSS in a max 1/2" bar for boring. Chowing it out with a ball mill first would make it less painful for sure though. I probably just want to use the broach/shape method because I just got an Advance cross-slide rotary, :drool5:

- cut me a break!

eKretz · Apr 27, 2020

implmex said:
Hi eKretz:
At the risk of seeming contrary here, how do you propose to get the nearly sharp corners in the pocket using the rotary table?
If the OP can tolerate radii in the corners, yes you could swing it out with a rotary table and a ball cutter, but if he cannot tolerate at least a 1/8" corner radius at each end of that pocket, the rotary table and a ball end mill will not get all the geometry.
This presumes the axis of the cutter is orthogonal to the axis of the pocket (as it would be if you surface milled it on a CNC)

As soon as you make the axis of any spinning cutter coaxial with the axis of the pocket you MUST make them concentric as well to get to the bottom of the pocket, and that means a tee slot cutter of maximum 1 1/4" diameter with a zero diameter shank unless you poke the shank through the bores before you insert the cutter.
As soon as you do that, you may not just stick the cutter out to the correct final diameter and turn on the mill...you'll break the cutter off as soon as it slams into the unmilled pocket.

So you would need to nibble it out bit by bit, growing the diameter by advancing the cutter a tiny bit each time so you can spin it and take a chip without snapping it off.

I do understand with the method you are describing that you never spin the cutter; you are using it like a shaper cutter and traversing from one pocket wall to the other...advancing the mill table to bring the cutter tip successively toward the surface you intend to machine as you swing out the arc using the rotary.
However, what your method neglects is what happens at the beginning of the stroke as the cutter needs to be forced into the workpiece and what happens at the end of the stroke as the cutter piles the chip into the bottom corner of the pocket.
If you have ever shaped a blind keyway on the lathe, you will recognize the problem: unless you've machined a relief groove or drilled a relief hole at the blind end of the keyway...with every successive stroke, the chip prevents you from getting as close to the bottom as you did with the prior stroke, and if you try to force it you eventually break the cutter.

So in theory, your approach can be made to broach out the OP's desired shape, but in practice, it sadly cannot, and when finishing the ends of the pockets (the inside faces of the ears, you cannot use a cutter other than a boring bar, with inserted tip run concentric to the bores and taking the whole of the face width in one pass.
You can sneak in with the smallest shank, largest diameter tee slot cutter you can rustle up to get some of it, but ultimately, you need a boring bar to catch the last bit of the inside corners of the pocket, and you NEED to poke the bar through the clevis bores.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Nope. I can tell you haven't used this method. Not surprising, it's pretty old school. You're not understanding what I'm trying to get across. The tool is just a plain piece of HSS, and it can most assuredly produce a nice radius and sharp corners, as well as cut the flat faces. If I had my equipment all set up and ready to go I'd make you a video. In the meantime I'll see if I can find a video or image that will help you visualize the process.

Scottl · Apr 27, 2020

Easy sleazy on a lathe.

Make a bar smaller than the two holes to be mounted between centers and driven by a lathe dog.

Drill a hole crosswise somewhere near the middle. Tap perpendicular to it for a setscrew.

Mount a small HSS lathe bit in the cross hole using a flattened piece of rod plus shims to get the cutting edge on center. The setscrew clamps the bit, which likely needs to be shortened.

Mount the part on an angle plate with the part centered on the centerline of the lathe.

You feed the cross slide in slowly and advance the carriage to the length of the cut, Then feed in another ten thou or so. You may need to back off the cross slide and readjust the bit for a larger radius.

It is slow and a bit tedious but it's an old school technique that's been done before.

What you will be doing is fly cutting the radius.

implmex · Apr 27, 2020

Hi again eKretz:
OK, so is your "shaper stroke" made by the rotary instead of the quill?
That's the only way I can see it working.
If so I assume too that you have a super solid spindle lock to keep the cutter from just spinning away from the load.

If I'm visualizing this properly, you are going to have one helluva muscular arm on the side that spins the rotary axis.
I assume you'd have to advance to cut depth, force the tool through an arc with the rotary, back the tool up a bit (to prevent scraping the tool on the backstroke), back up the rotary, advance the tool again, drop the table down a bit swing the arc with the rotary again, back up the tool, back up the rotary, drop the table a bit advance the tool swing the rotab...etc etc.

My arm is starting to ache just thinking about it, but I assume there's no reason you can't just disconnect the worm and bolt a big handle onto the table of the rotary so you can swing it fast, by hand.

You know that could WORK!
Very clever indeed...I owe you one for not seeing your logic and I learned a cool new trick today.
Sadly I'll never get to use it...I have a sinker EDM

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

eKretz · Apr 27, 2020

implmex said:
Hi again eKretz:
OK, so is your "shaper stroke" made by the rotary instead of the quill?
That's the only way I can see it working.
If so I assume too that you have a super solid spindle lock to keep the cutter from just spinning away from the load.

If I'm visualizing this properly, you are going to have one helluva muscular arm on the side that spins the rotary axis.
I assume you'd have to advance to cut depth, force the tool through an arc with the rotary, back the tool up a bit (to prevent scraping the tool on the backstroke), back up the rotary, advance the tool again, drop the table down a bit swing the arc with the rotary again, back up the tool, back up the rotary, drop the table a bit advance the tool swing the rotab...etc etc.

My arm is starting to ache just thinking about it, but I assume there's no reason you can't just disconnect the worm and bolt a big handle onto the table of the rotary so you can swing it fast, by hand.

You know that could WORK!
Very clever indeed...I owe you one for not seeing your logic and I learned a cool new trick today.
Sadly I'll never get to use it...I have a sinker EDM

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Yes, now you've got it. And yep, absolutely disengage the worm and use a bar! Of course, the EDM would be a smidge easier...

Need ideas to mill a radius botom pocket, no cnc.....Help please

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