Need a suggestion for large part workholding

Machinerer · Dec 28, 2021

Seems pretty simple, but I have a large hogout, aluminum, 26.5"x15.5"x6.5". It's about 200lbs. For the very first operation, the operator is hand drilling/tapping 5 holes in the part, and I'm trying to take some work off of the operator, and he is already very busy running multiple machines. This fixture was originally designed using the clamps you see in the screenshot(Carr-Lane CL-15-SAC) however from the way they feel, I have about zero confidence in these clamps, especially considering this part is being roughed very aggressively in an HMC, so I'd hate to see 200lbs of aluminum fall on spindle moving 300ipm. I ended up putting 4 holes in void areas of the part, which I put 1/2-13 studs in, and thru bolt them through the fixture. Good thing I did, because after roughing the first part, all of those clamps had vibrated loose. My question, is does anyone have suggestions of a better way to hold this part, that would give me a little more confidence, and take the hand drilling off of the operator?

The part cannot stick off the tombstone any more than it already does, whatever workholding is used cannot be any higher than an inch along the outside perimeter. I appreciate any suggestions!!

implmex · Dec 28, 2021

Hi JBethell:
Do I assume correctly you want to avoid all pre-op machining and just plop your part against the tombstone so no dovetails, no through bolts, no tee slots no nothing.

That to me means Mitee-Bite Pitbulls: the more around the periphery the better.
Your part as shown is relatively low profile, so the cantilever forces are much lower than if this thing stuck up in the air 18 inches.
If you wanted additional security, you could locally dovetail or tee slot the blank after mounting, and add additional clamps between the Pitbulls and then go to town on it with pretty good confidence.

Yeah, it's a pain in the ass to do up all those screws, but as you say, a 200 pound block loose on the machine is not a happy thought.

Cheers

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

Shawnrs · Dec 28, 2021

I agree with the pitbulls, they will hold the part in pretty snug but sometimes the part will spring with you release them.

Another thought could be is using two vises and placing softjaws on the outside and use those to secure the stock. It may help using knife edge softjaws.

dandrummerman21 · Dec 28, 2021

I have an idea, perhaps dumb, but maybe it would work for you, utilizing your existing setup as pictured.

You mention the clamps vibrated loose. Did they actually vibrate loose, or was it perhaps from the part flexing and getting crushed after it was roughed out that contributed to the looseness?

On a similar edge clamping setup that I use from mitee bite, there was one time when I couldn't get the clamp to stay put. So after clamping it in place, I put a toe clamp directly on the body of the edge clamp so it couldn't slide back. I suggest you could maybe do the same if you have room for your tool path around the periphery.

Vancbiker · Dec 28, 2021

Why have the hand drilled/tapped holes? Put that op on a clapped out VMC. Perfect Fadal/Haas type work and good for a trainee employee. Will be done in a few minutes per part.

I'd skip the Carr Lane edge clamps. The Mitee Bite products suggested above are much better IME, particularly if you add a small dovetail feature.

Without knowing what all is being done to the part and what quantities need to be run it is tough to gauge how elaborate of suggestions to make.

Machinerer · Dec 28, 2021

dandrummerman21 said:
I have an idea, perhaps dumb, but maybe it would work for you, utilizing your existing setup as pictured.

You mention the clamps vibrated loose. Did they actually vibrate loose, or was it perhaps from the part flexing and getting crushed after it was roughed out that contributed to the looseness?

On a similar edge clamping setup that I use from mitee bite, there was one time when I couldn't get the clamp to stay put. So after clamping it in place, I put a toe clamp directly on the body of the edge clamp so it couldn't slide back. I suggest you could maybe do the same if you have room for your tool path around the periphery.

That's a good thought, that maybe it's actually the part deforming. I did drill/tap the top and bottom of the plate, so the edge clamps are backed up to washers to prevent them from sliding. like this, but i'd much prefer to get rid of them altogether. Just doesn't feel safe.

Machinerer · Dec 28, 2021

Vancbiker said:
Why have the hand drilled/tapped holes? Put that op on a clapped out VMC. Perfect Fadal/Haas type work and good for a trainee employee. Will be done in a few minutes per part.

I'd skip the Carr Lane edge clamps. The Mitee Bite products suggested above are much better IME, particularly if you add a small dovetail feature.

Without knowing what all is being done to the part and what quantities need to be run it is tough to gauge how elaborate of suggestions to make.

I agree about skipping the edge clamps. They weren't my idea, and I have never liked that style of clamp.

Are you saying to put the "Prep op" on a VMC? That was my original idea, but most of our parts are small and so we don't have a VMC with a crane nearby.

As i mentioned in the reply above this one, pitbulls might work, but I'd have to make something to let them move, to give them more travel.

The part is very complex. Ends up right around 18lbs when it's all done. Customer is paying WELL into 5 figures per part, and we should be making 20-30 per year, so money invested isn't a huge factor. Maybe I'll push the VMC idea, and sell them on the value of adding a crane somewhere.

Machinerer · Dec 28, 2021

implmex said:
Hi JBethell:
Do I assume correctly you want to avoid all pre-op machining and just plop your part against the tombstone so no dovetails, no through bolts, no tee slots no nothing.

That to me means Mitee-Bite Pitbulls: the more around the periphery the better.
Your part as shown is relatively low profile, so the cantilever forces are much lower than if this thing stuck up in the air 18 inches.
If you wanted additional security, you could locally dovetail or tee slot the blank after mounting, and add additional clamps between the Pitbulls and then go to town on it with pretty good confidence.

Yeah, it's a pain in the ass to do up all those screws, but as you say, a 200 pound block loose on the machine is not a happy thought.

Cheers

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

Wow, I swear I replied to your post way earlier. In any case, yes, eliminating the prep would be optimal. The guy who runs the parts is our best operator, but he's about 5'1" and MAYBE 115lbs, so him trying to wrestling these parts to hand drill/tap them isn't optimal. Maybe something as simple as a drill jig plate with drill bushings would be the easiest, most practical way. If I can get this thing on a VMC, that would be best, but we don't have cranes at every machine.

And yes, the screws are definitely nice for piece of mind.

Vancbiker · Dec 28, 2021

JBethell said:
......Are you saying to put the "Prep op" on a VMC? That was my original idea, but most of our parts are small and so we don't have a VMC with a crane nearby.......

Sorry, I did not take lack of a crane into account. Shop I retired from had many of the machines under 2 and 3 ton bridge cranes and we had half a dozen or so portable 1/2 ton jib cranes we could move to machines not served by the bridge cranes. Kind of like this...

Portable Jib Cranes - Product Page

Since we had those capabilities, I overlooked that some shops are not so well equipped.

JBethell said:
.......The part is very complex. Ends up right around 18lbs when it's all done. Customer is paying WELL into 5 figures per part, and we should be making 20-30 per year, so money invested isn't a huge factor. Maybe I'll push the VMC idea, and sell them on the value of adding a crane somewhere.

The above suggests that there probably are details to be machined on the face that is resting on the fixture plate. Possible to generate some of those features and as well as the tapped holes and add a couple tooling holes in a VMC prep op? The tooling holes would be used to locate with a round and diamond pin for the HMC op.

Machinerer · Dec 28, 2021

Vancbiker said:
Sorry, I did not take lack of a crane into account. Shop I retired from had many of the machines under 2 and 3 ton bridge cranes and we had half a dozen or so portable 1/2 ton jib cranes we could move to machines not served by the bridge cranes. Kind of like this...

Portable Jib Cranes - Product Page

Since we had those capabilities, I overlooked that some shops are not so well equipped.

The above suggests that there probably are details to be machined on the face that is resting on the fixture plate. Possible to generate some of those features and as well as the tapped holes and add a couple tooling holes in a VMC prep op? The tooling holes would be used to locate with a round and diamond pin for the HMC op.

The previous shop I worked at had a gantry crane at pretty much every machine. At this shop, we have some of the best machines available, however sometimes I think management believes that machine and tools are the only components to making parts. Some features could definitely be machined on a VMC prep op like you're saying, though I'd have to see if there'd be much benefit, as due to side work on the 12:00, 3:00, 6:00, and 9:00 sides, I THINK 2 HMC roughing operations will be necessary anyways. I'll have to take a closer look at whether we might benefit from some roughing on the VMC. Thanks for the suggestion!

implmex · Dec 28, 2021

Hi again JBethell:
My description of what I had in mind was a bit unclear, so here's a slightly more detailed version.
Make your fixture plate with a good number of Pitbulls around the periphery.
Mount your block with the Pitbulls.
Buy or make a tee slot cutter on a long enough shank that you can get close to the fixture plate even with the 6.5" thick block clamped in the Pitbulls.
Punch the tee slot cutter into the sides of the block by a quarter inch or so, just like a Woodruff keyseat between the Pitbulls and close to the fixture plate, say 3/8" above the fixture plate.
Make up some toe clamps with the reverse of the Woodruff profile on their noses.
Mount those in the slots you just milled in the block and snug them down.
Leave the Pittbulls in place for a bit of extra hold and then go crazy on your part.

BTW, The screws I was referring to in my first post were all those you have to snug up to clamp all the Pitbulls, not the ones you were using for your trial part. (I didn't make that very clear...my bad)

The way I'm describing, you don't need a second machine, you don't need a second crane, you just need a decent sized saw on a long enough arbor and a quickie program to run the saw.
Making 4140 HTSR clamps is child's play and if you put a few of them around your part, you'll really have to make a major screwup to rip the block back off the tombstone.

Cheers

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

Machinerer · Dec 28, 2021

implmex said:
Hi again JBethell:
My description of what I had in mind was a bit unclear, so here's a slightly more detailed version.
Make your fixture plate with a good number of Pitbulls around the periphery.
Mount your block with the Pitbulls.
Buy or make a tee slot cutter on a long enough shank that you can get close to the fixture plate even with the 6.5" thick block clamped in the Pitbulls.
Punch the tee slot cutter into the sides of the block by a quarter inch or so, just like a Woodruff keyseat between the Pitbulls and close to the fixture plate, say 3/8" above the fixture plate.
Make up some toe clamps with the reverse of the Woodruff profile on their noses.
Mount those in the slots you just milled in the block and snug them down.
Leave the Pittbulls in place for a bit of extra hold and then go crazy on your part.

That's not a bad idea. I actually have a few slot mill's already in the machine that would work for this.

LostFab · Dec 29, 2021

Could you use a dovetail bit in a hand router to mimick Marcus' idea and give you a positive locking feature without any pre-op machining or oddball tools? Router and bit from horror freight probably cost <$50 if you don't have anything on hand...
I've seen a shop that runs all their blanks across a router table doing this, but they're in the 5-15lb range so easier to manhandle...

Machinerer · Dec 29, 2021

LostFab said:
Could you use a dovetail bit in a hand router to mimick Marcus' idea and give you a positive locking feature without any pre-op machining or oddball tools? Router and bit from horror freight probably cost <$50 if you don't have anything on hand...
I've seen a shop that runs all their blanks across a router table doing this, but they're in the 5-15lb range so easier to manhandle...

Damn, that's actually a pretty slick idea. Is that something you'd be able to manage by hand? Never tried cutting aluminum with a hand router.

Vancbiker · Dec 29, 2021

Lots of places use a router to put radius edges on parts. If the sawn edges are good I would think dovetails would be ok.

mhajicek · Dec 29, 2021

I think in aluminum it should work fine. Conventional cut so it doesn't pull you into the cut.

implmex · Dec 29, 2021

Hi All:
To those who mused about prepping the block with a router and a dovetail bit, it's a good idea if you don't have another way, but you have a nice big horizontal just standing there, ready to go.
Why not use it?

You only have to handle the stock one time, you get however many ponies the machine has to offer in order to make the cut, and you can control it, so it's safe and quick.
You can also make the noses of the clamps match the slots, and if you put in your Woodruff slots above the Pitbulls you don't even need to care where they are.

I'll bet it's faster and easier and more secure to do it on the machine.

Cheers

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

Trevor360 · Dec 29, 2021

Here is a potential idea:
1)Use your edge clamps to hold the part with no bolts
2) First operation in the program swing the B around to 180 and drill and tap the part through your fixtures clearance holes
3) M0 in the program with a comment to add bolts
4) Begin your heavy roughing

LostFab · Dec 29, 2021

If you can use the existing op 1 fixture and some existing long tools to cut clamping features or bore bolt holes like Trevor360 mentioned that's going to be more efficient, in this case with low volumes and high margins that probably makes sense to buy tools if they didn't have them. Just wanted to pitch the idea that banging out blanks with a hand/table router would work in a pinch for some applications...Especially if you have some free hands while a machine is busy cutting parts...

Rstewart · Dec 31, 2021

Also just in case you didn't know, your material needs to be pretty square for those edge/toe clamps to hold securely. I learned the hard way once.

I still don't trust them for roughing IMHO

Need a suggestion for large part workholding

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Cast Iron

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Aluminum

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Aluminum

Aluminum

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