Part Fixture ?

[M. Anderson]

Ok folk’s – I need some help (maybe in more ways than one!)

 

In the shop we run some small .750 +/-.0005 OD TGP by .200 thick – 1045 solid disks – turned on the lathe. I have no live tooling on the CNC lathe so we have to move them to the CNC mill and poke in 6 equal spaced holes – with chamfers on both sides.

 

No big deal, just run them in a 5C-collet holder and flip them over for the other side, and the collet holds them flat and square to the OD.

 

We usually just run a few (less than 100) at a time.

 

Now the customer needs 1000’s of these things a month, not the usual 50 or 60 per order!

 

Problem is I need to come up with a way to fixture these, other than in a collet.

 

The mill table won’t hold a 100 collets at a time!

 

Problem I am having is the part is lifting, or it is cocking, in what I have tried so far. The part is so thin, and I am trying to grip on the OD as holes are .0005 tol./parallel to the ground OD on the bar stock.

 

Anyone have any miracles for holding bunches of small thin parts - FLAT???

 

Open for suggestions?

 

Thanks,

 

Mark

[mayday]

wow mark bummer,

have you looked into sinker edm?

maybe make some electrodes in sets and have the holes burned? what size are the holes?

im

[thoskins]

have you tried machining some soft jaws for a kurt vise?

[M. Anderson]

MayDay,

 

Yea we used to sink'em - years ago.

 

But the EDM's we have are early 90's, kind of slow?

 

Holes are .116 +/- .001, so reamed is good enough.

 

I never thought that holding a bunch of these at a time would be such a PAIN in the *SS.

 

Later, Mark

[M. Anderson]

thoskins,

 

Yea, that was the first thing I tried.

 

Still not sure if all this is not just operator error, I am going to run some in the morning and see if they lift on me. But two different guys are saying the parts are lifting or not seating square in the fixtures?

 

Thanks guys,

 

Mark

[one shot]

Mark,

I have done very simular parts. The soft jaw option worked for me. I cut an undercut with a dovetail cutter relieving about 1/2 the bottom of the pocket milled in the jaws. I cut the jaws with an .080 shim between the jaws and tightened the gibb adjustment to eliminate movement.

[MetalMarvels]

I have also used these Mitee-Bite products very successfully for large run production. They are a bit of a pain to set up (to much so for a short run) but they hold well and you can pack a lot of them in a small area. One bad part is that they are a little pricey. One good part is that they are great for fixturing a repeat job if you put them all on a base plate that you can index to your mill table.

 

http://www.miteebite.com/

[Chris Rizzo]

oh yeah, dovetail the softjaws to give you some downforce. What about a vacuum plate? Sounds like just light machining, you certainly could load a lot of them at once on a dedicated fixture/vacuum plate. I've been waiting for the right part to build one here, but I know a few of the other fellas on the forum use them.

 

HTH, and let us know what works.

[Tim Johnson]

quote:

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I have also used these Mitee-Bite products very successfully for large run production.

---

We use them successfully running much smaller quantities. They are well worth the price. If you have an indexer you can make/buy a tombstone, make 8 fixtures and you can reload parts on 4 fixtures offline while you're running 4.

[robk]

Why not hold them on the (electro)magnetic plate? Have a couple of those made with .100 deep blind bores to locate your parts in. Pre-drill bigger .dia holes under the location of your .116 dias. Machine a couple of stops on the machine table and butt-up the plate against them. Throw the switch on. Now all you have to do is probe or indicate the location of the plate and hit that green button. The investment might be a little bit more up front, but it will pay for itself in no time by the amount of parts you will run. It will save you set-up time (virtualy none) and by having 2 plates one could be loaded/unloaded with parts while the other is running.

Also, if you have the capability use solid carbide drills and you could get rid of the spot drilling and reaming operations (use quality tooling).

[Tom Dorgan from American Precision]

If you can I would definately try a vacuum plate fixture. Since I am a router guy that is all we use and it sounds like you have enough quantity to justify buying a small vacuum plate.

[medaq]

If you do the softjaw option, invest in a inch lb torque wrench, so the varying operators still clamp with identical force. Releiving alot of your headaches.

 

JIm

[medaq]

Also be careful with mitee bite type clamps. They do a good job. But if you want to rack alot of parts up. The accumulation of clamping force can be quite significant. And start to warp your fixturing.

 

 

Jim

[Guest CNC Apps Guy 1]

quote:

---

...If you do the softjaw option, invest in a inch lb torque wrench, so the varying operators still clamp with identical force...

---

Can I hear an AMEN!!!!????

 

In. Lb. Torque wrench would eb mandadory for something like this. Not too pricey either. You may have to experement a little bit with what pressure works well enough. Use a .0001 indicator on the top, and the bottom. Clamp until you use up 50% of the tolerance, then back off a smidge.

 

JM2C

[Tom Dorgan from American Precision]

+++10000 on the torgue wrench. That way every operator tightens the parts exactly the same. Take operator error out of the picture whenever possible.

[CAM-mando]

I see the .0005 paralellism which isn't that big of a deal on a .200 thick part, but what is the True position requirement of the holes ?

 

For thousands of parts per month I would be looking at a palletized fixture concept if possible. Since the operator can load a pallet while the machine is running. I dont know if the hole spacing allows it, but possibly a simple clamp plate over the part with the part in a close dtolerance c,bore.

 

We use a simple Midaco pallet system on our verticals for these type applications.

Midaco Manual Pallet

[M. Anderson]

WOW GUY'S!

 

Thanks for all the input!

 

Been gone most of the day – wife buying a new car!

 

I did run some this morning - in a soft jaw vice.

 

The only way I got a part to lift was if you had the vise extremely tight, then you would have a problem with the parts lifting. So, these idiots must really be hammering it closed!

 

I can look at the vice jaws and tell they were not paying much attention about how tight they were getting things. Some of the pockets were mauled up a little.

 

Anyway, I think I will look into using some of the “Mitee-Bite” clamps and make up some kind of pallets as some have suggested, that looks like a good way to run this quantity of parts.

 

Plus – I am going to invest in some torque wrenches!!! These guys are NUTS!!!!!!

 

Thanks for all your input!

 

This is one he!! of a knowledge base!

 

Thanks again,

 

Mark

[medaq]

I even have my guys torque wrench the screws for the mitee bite clamps

 

Jim

[MetalMarvels]

+10,000,000 on the torque wrench. It is absolutely the only way to get repeatability between operators. I have even been guilty of starting the day by "torqueing" the vise handle pretty good and by the end on the day I am only hitting about half the force I started with. The torque wrench makes it a "no-brainer".

 

0.750 diameter is a bit small for a good vacuum hold IMO - especially when poking holes through it (reducing the vacuum surface area). I have gotten good results down to about 1-inch by 2-inch with holes near the edges. Smaller plates tended to walk up the drill bit and break the vacuum.

[Müřlıń®]

Make sure your vice has no slop first.

 

You could run a tool at 0 rpm that went in there and tamped them down first. We used to use this plastic for stripping the parts off punches instead of using springs. It will compress and prol wouldnt stall the z servo. It would push the parts down in the vice so you could gang a bunch of them at a time.

[MCam Newbie]

Interesting. I have similar applications in Inconel X750. We use a precision tool-makers vise ("square to the world" .0002, movable jaw pulls closed and down with allen bolt through jaw), to hold our fixture. We use three .75 thick x 2.5 high x 6.0 long precision gound rectangals. They have a dowel pin through at each end, and the inside faces are countersunk and hold bevel spring type washers that push the blocks apart, but will allow them to be pressed solidly against each other when clamped into the vise, to facilitate part removal

Then we place .002/.003 thick brass shim stock between the faces, clamp the blocks into the vise,

and machine counterbores to part nominal diameter.

These counterbores centerlines are on the 2 seams where the outter blocks contact the center block.

Also machine hole pattern with some tool clearence. Remove the shim stock, and the blocks hold our parts, 10 or 12 at a time, in 2 rows.

Only difference is I hold the part O.D. to .0005 total deviation. The parts stay flat, I have some counterbores that are +.003/-.000 deep, and have no problems. I did find that I had to radius the "corners" at centerline, where the blocks meet, slightly, to avoid marking the O.D.s of the part. Have run many hundreds of parts with this holding method, using 2 fixture sets. As one is in the machine, the secons one is being unloaded, cleaned, and reloaded, so the spindle stays in work. I do some profiling on pockets, and never have had a part slip rotation-wise, or pull up.

One note: The dowel fit should allow a light hand press fit. The blocks must all locate solidly along the bottom, with faces parallel within a couple of tenths.

We used A2 steel, and heat treat after proving the tooling, so wear is not a worrisome factor.

They work so well, we had several sets of "blanks" made up, and ready to use. If the dowels are 1/2 way up the blocks, both top and bottom can be used for different size parts, and accuracy is not affected.

This is especially nice when the job comes back, as workholding set up is minimized. My vise always returns to the same location on the machine, within .0005 or better, so my setup man only has to pick up tool length offsets. Coordinates (G54, 55, etc.) are loaded with G10s' at start of the part program.