Circle Milling

[GlennW]

I can't believe no one has suggested soft jaws! If the material is rectangular chuck it in a four jaw chuck and turn to the correct dia then part off oversized. Turn up some soft jaws and finish the back side in them. I do it all the time with soft jaws and have been successful as thin as .04" thickness.

He's cutting them from a rectangular piece of sheet, not bar stock.

[Bentworker]

I'd use a lathe with the previously mentioned method or I would go "Clickspring" and superglue it to a turned aluminum chunk that is held in the chuck of your lathe.

[asallwey]

Just a bit more info on my original objective. The 1/8" rectangle was 6" x 9" and I was asked to get as many disks as I could. The final disks needed 4 holes equally spaced near the center.

Wes, the video was very good! I believe it demonstrated what Glen described, just using different materials. I will put it on my list of techniques to try when I get a chance.

Ok, my side relief was inadequate so I increased it. With my current "play" setup (above) there was less squealing and chatter. I did note the caution about the cut piece moving, so I think I'll shift to the lathe as Glen said.

Thanks for the help!

[Mr Ron]

I think an easier way of doing it, especially as it is aluminum, is to double stick tape a rough cut disc of aluminum to a smaller diameter piece of plywood that has a pivot hole in the center. By rotating the disc/plywood assembly around the pivot point against a disc or belt sander, a smooth aluminum disc will result. I have done this after trying to do it on the lathe or mill. I don't like working wood on either machine, so sanders do what they were designed to do. Actually, by sandwiching the aluminum between 2 discs of plywood, the whole thing can be cut on the band saw and cleaned up on the sander.

[John Hasler]

asallwey writes:
> Just a bit more info on my original objective. The 1/8" rectangle was 6" x 9" and I was asked to get as many disks as I could. The final disks needed 4
> holes equally spaced near the center.

What diameter?
Could you saw out disks with a hole saw? Then you could finish them to exact size as I suggested with minimum waste. You could also drill them as a stack.

Bentworker suggested superglue rather than tape: that's a good idea. It's stronger, and a bit of heat or a night soaking in acetone gets rid of it.

[RSG]

I can't believe no one has suggested soft jaws! If the material is rectangular chuck it in a four jaw chuck and turn to the correct dia then part off oversized. Turn up some soft jaws and finish the back side in them. I do it all the time with soft jaws and have been successful as thin as .04" thickness.

He's cutting them from a rectangular piece of sheet, not bar stock.

If sheet then yes it would be tough to put in a four jaw, but he could glue them to a turned faceplate and machine them then finish the other side with softjaws as I mentioned.

[Patio]

What is the finished diameter of the disks?
How many do you need to make?

I like Glenn's and Harold's method best.
The size will help determine how they need to be held, and how many, would make a big difference in the method I would use.

If many were needed, and using the friction drive method, I would go as far as to super glue the wood pressing fixture to the live center. Maybe even make one for the chuck too.

No mention has been made about the surface finish of said disks. I believe that is what Harold was alluding to, when he mentioned using softjaws, in the lathe. A finish pass could be made, on each face, of the disk if required.

Once they are all turned to size, I would turn my, mill's vise jaws, in the lathe, to create a set of softjaws for the mill. That would allow me to drop the disk into the recess of the softjaws and drill or bore if necessary, any required holes, very quickly.
Soft jaws are a wonderful thing!

Hope to hear how you make out, either any way you do it.

[asallwey]

Sorry for not responding sooned. The disk diameter was 2.8" and it had to fit into the back of a cabinet.

I did talk him into allowing a center hole, so after cutting the disks on the bandsaw I bolted them to a bar and used the lathe to turn the OD. Then loaded them into the 3 jaw and bored the id I needed.

But the original plan was to make disks that I couldn't center bolt. The suggestions you all have provided will be what I will try, just for fun and a learning experience now. The video sort of demonstrated what Glen and others said.

Again, I really appreciate the help.

[asallwey]

Just a follow-up to this thread.

I did further reading and video watching based on the leads folks provided. I am always fascinated by the breath of work in a given topic. I saw small, thin washers made, and I saw 30' x ??" bars being trepanned -- Wow!

I finished my project of 3 disks, they looked good and measured out very well. Now I was asked to make another 6, again from plate. This time I was armed with all the knowledge you folks (and the all-knowing internet) provided, so why not put some things into practice.

I did my layout on the plates, drilled 3/8" center holes for an arbor, rough cut the disks on the band saw, stacked them on an arbor (a bolt), center drilled the arbor to use a live center, and turned the od to dimension -- piece of cake! But the WD40 made a stripe on my wall, will need to address liquid containment. Just another tangent!

Bought some soft jaws from Monster Jaws for my 6" Bison, made a disk slightly smaller than disk OD to clamp in the soft jaws so I could bore them (may try Harold's nut next time), left a step at bottom of jaws for disk positioning, loaded my disk stack in anticipation of opening the center hole (currently 3/8") to final dimension of 1.2" -- I'm cooking now!

O, O, I can't reach my disk stack! I have my 5/8" drill chuck with a 1/2" drill in the tailstock, and it doesn't reach! I'm hit with a confluence of bad luck -- the jaws are kind of high and long, and being reversed drop below the level of my compound. Also I have my dro mechanism mounted to the left side of the compound and it adds almost 2" to the left of the compound. So I can't use a drill, and my small boring bars are too short, never had this problem before, so -- plan B.

Remove the stack, move to the mill, mount my rotary table on which I've mounted my old 3-jaw (with steel jaws), and gently clamp 1 disk, center it using the 3/8" hole, then swap in 2 other disks to see how close they are centered. Ok, within 0.010", so that will work as they will return to the lathe for final boring. Drill each center hole 11/64" (no reason for this size, just looked good) so I can use my 1/2" boring bar. Job done, no blemishes on od, back to the lathe.

Disk stack back in soft jaws, spin it up to see how everything looks. Whoa! Those soft jaws are impressive spinning away there, better not go too fast, turn vfd down from 300 to 250 rpm. Boring bar in, not going to hit anything, so ease into the hole. Wait! Outer disk seems a tad loose, shut down and investigate. Seems the outer 2 are not as tight as inner disks, pull off 3 leaving 3. Maybe I should have bored the soft jaws with a tiny taper to compensate for bending or shifting. Ok, 3 disks clamped, bore out hole so all 3 are the same, stop and measure, now finish to dimension.

You realize all of this has taken a lot longer than I anticipated, and I usually double or triple my time estimate. So, you guessed it, time to speed things up a little. Initial cuts have been toward the chuck and were great, so I start cutting coming out. I'm taking 0.010" per cut each direction. Hmmm, I see some separation between the outer 2 disks. Stop and think, do I pull them out, clean up the edges and start over? I decided to continue boring, but only going in, gap did not grow and they seemed to be holding, but it was clear that material was in each gap. I was cutting dry and noticed that my insert was getting a gob each cut and the finish looked like crap. Apply WD40 and forge ahead, no more gobs and finish looked good, dimension reached, debur the inside of each disk (grrr), this part done. Learned not to speed things up. The final 3 disks will be cut only going inward, end of tunnel is close.

It's not easy being a hobbiest!

Thanks again for your advice,

Alex

[Harold_V]

The chance that holding more than one piece at one time in soft jaws is not good. Because they are fast and easy to use, once properly prepared, run parts one at a time only.

There's issues with soft jaws that must be addressed. One is rapid rotation can cause jaws to release parts. Heavy jaws make the problem worse. If you're doing work on thin walled material, you may not have the option of tightening the jaws enough to overcome what folks like to call centrifugal force.

When you bore soft jaws, it's important for the spider, or other material used for setting the jaws, to be as far towards the outer ends of the jaws as possible. That's due to the clearance in the slides for the jaws, which permit the jaws to tilt outward as pressure is applied. If you don't load the jaws in identical fashion, they'll grip ONLY at the most inward position. That should help you understand why you shouldn't hold more than one part at one time.

You don't have to have a center hole to machine a disc. If the blanks have sufficient material, they can all be turned at one time by pressing with a live center. I used to machine ten contact lens blanks at a time by that method. Works just fine, and is quite fast. Aligning them for machining is easy if you have the pressure plates turned to the finish diameter, so they become the guide to locate the parts before pressure is applied.

H

[asallwey]

Harold,

I've seen the advice about positioning the spider as far out as possible. So if the soft jaw is 2" high, and the work piece is 1/8" thick, where in the 2" span would you want to hold the work? I bored the jaws to about 3/8" from the bottom (width of the disk I made for boring the jaws) and put a step in. This held 3 pieces very well. From what you say I was probably lucky, or at least pushing my luck. I 'm glad you described how the jaw would move, I never thought about them tilting.

Thanks again,

Alex

[Harold_V]

Harold,

I've seen the advice about positioning the spider as far out as possible. So if the soft jaw is 2" high, and the work piece is 1/8" thick, where in the 2" span would you want to hold the work?

Unless there's reason to bore deep, I prefer to grip at the outer edge of the jaws. That keeps tools short and prevents working deep inside, where you may have a chance of hitting the jaws on the cross slide or compound. That's assuming you're not taking aggressive cuts, where you could benefit by gripping deeper in the jaw. Another benefit of using the outer edges of the jaws is jaw life. The less you have to remove from jaws, the longer they'll serve you. That's one of the reasons I use the spider---I can reset previously machined jaws and lose only a few thou. I have soft jaws I've been using for more than 40 years.

I bored the jaws to about 3/8" from the bottom (width of the disk I made for boring the jaws) and put a step in. This held 3 pieces very well. From what you say I was probably lucky, or at least pushing my luck. I 'm glad you described how the jaw would move, I never thought about them tilting.

A great deal depends on the cuts you intend to take. If you're roughing, pretty good chance a part will slip, maybe even come out. With light cuts, that may or may not be an issue. Also, how closely you hold the parts (in diameter) will help determine your degree of success. A part a few tenths smaller than one next door may slip. Or not. It's just that unless you take very light cuts, there's always the risk of a part slipping, which often damages the cutting tool. For me, it's not worth the risk, but there may be occasions where it can be done with success. Consistency of part size is ultra important if that be your quest, however, as would be properly (heavily) loading the jaws before machining to size, to ensure that they have all the slack removed from the slides, and are machined in perfect alignment with the part(s) to be gripped.

H