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John Stevenson
07-01-2009, 07:52 PM
Decided to make some eccentric clamps to match der operator.

Got a job in from a well know aero engine maker who wishes to remain anonymous but has RR in the name.

Three bars with pegs to go into holes that act like a simple 3 jaw chuck to hold a turbine blade in the crack detection tank, nothing critical, no flight safety crap and you can put any non ferrous metal into these tanks.

However this anonymous company decided they need these bars making out of 30shïtfacedrockhardtoolcrunchy stainless steel.

Unfortunately this grade is only sold in sheared strip and not cold rolled with the result that [a] it's not flat, [b] the edges are rounded where it's been sheared and [c] it's the most terrible material known to man or beast and [d] it's not magnetic.

So they want the bottom face machined flat, all over.
No good clamping to the bed and doing it is stages as when the claps are released it will still be bent, soooooo I need to hold it by the edges whilst I mill the whole side in one go.

Now I have seen these Mighty Bite clamps before in pictures but never in the flesh, looked them up in MSC J&L and had to lean on the battery charger to get some resuscitation back into the circuit, [ damn Lucas pacemakers ]

Seventy freaking nine pounds each ????????????????? leastways I think each as there is no picture.

Soooooooooo, raid the scrap box and mill 4 long tee nuts, tap for one Allen screw and one grub screw. Bit one done

Lob a chunk of 22mm bar [ 7/8" to the metrically impaired ] in the chuck with three bits of banding under one jaw to throw it off centre, drill and ream to 5/8" to fit head of 10mm Allen screw, loctite and whack onto head of screw with large bopper. Bit two done.

Find long U bolt nut off 32 tonne trailer, bore 22mm and part off 4 pieces. Bit 3 done.

All bits present and correct on duty.

http://www.stevenson-engineers.co.uk/files/eccentric_clamp1.jpg

Did some spare Tee nuts at the same time.

Shot of the setup.

http://www.stevenson-engineers.co.uk/files/eccentric_clamp2.jpg

Three fixed fingers at the rear, eccentric clamps at the front with some normal tee nuts to act as spacers and be lower than the top face.

http://www.stevenson-engineers.co.uk/files/eccentric_clamp3.jpg

Close up of the clamp, you place the clamp, nip the grub screw to hold the tee nut into position then wind the Allen screw round and the eccentric forces the hexagon piece against the work.

Doesn't need to be hexagon, could be square the main bit is the eccentric action.

.

camdigger
07-01-2009, 07:59 PM
So the eccentric locks by friction? I don't see why the eccentric doesn't release with cutting vibrations?

If it works, it sure seems like a neat solution to a tough clamping problems.

ligito
07-01-2009, 08:01 PM
Good lick, John.:)

John Stevenson
07-01-2009, 08:06 PM
Probably would come loose if you went all out to try to rip this off the table, however I have too much time invested in these arms what with the slot details that are on the underside and the rack teeth to get it too excited.

Probably took 1/2 hour to flatten all three, took nearly two hours to make the damn clamps.

Thinking about it it works the same way as a camlock chuck and they work out OK until you get big interrupted cuts.

motorworks
07-01-2009, 08:45 PM
Nice Work.RR will be proud

I sprung for the "real thing" aka "Mighty Bite your wallet", but billed them
out to the job I was doing :)
Noticed that they are now copied by Phase II for about 1/3 the price
Not sure of the quality.

Yes they hold well up to a point and then...
Had a nice job in the cnc mill that was about finished when
it came loose. Came up with a few new swear lines...
Put those in me note book as well. Never know when I my need that combi
again.
eddie

gambler
07-02-2009, 01:46 AM
thats a cool clamp. nice work.

gearedloco
07-02-2009, 02:37 AM
So the eccentric locks by friction? I don't see why the eccentric doesn't release with cutting vibrations?

If it works, it sure seems like a neat solution to a tough clamping problems.

I was wondering about that too. Maybe a setscrew (with brass tip)through the hex might solve the "obvious" problem. Hey - with a little effort I could make this really complicated!

-bill

Evan
07-02-2009, 08:37 AM
You should try some like this John. The black one is hardened steel held by a flush socket head cap screw and is tightened against the work with an angle grinder spanner as you lock it down. It can be flipped over so that vibration tends to tighten the holding screw for the tough jobs.

http://metalshopborealis.ca/pics3/engclamps.jpg

John Stevenson
07-02-2009, 08:57 AM
Interesting concept Evan, that's given me an idea on an improvement, mind if I pinch the basic design ?

.

Evan
07-02-2009, 09:05 AM
Not at all. I'll be interested to see what you come up with.

To save you some time here is a DXF of the cam profile:

http://ixian.ca/server/camclamp_profile.dxf

GadgetBuilder
07-02-2009, 11:39 AM
Nifty concept Evan.

For those of us sans CNC, it looks like a slice of round stock with a hole drilled off center could substitute for the cam. Leaves room for extra spanner holes giving more options for the handle angle while securing.

John

RancherBill
07-02-2009, 12:29 PM
Here's the second pic for the cdcotools system.
http://cdcotools.com/morepics.php?itemid=477

Evan
07-02-2009, 01:16 PM
For those of us sans CNC, it looks like a slice of round stock with a hole drilled off center could substitute for the cam. Leaves room for extra spanner holes giving more options for the handle angle while securing.


I haven't tried it but I don't think a circular cam will work as well. I designed the spiral cam to have the clamping force vector pass through the bolt hole at all angles of rotation. This prevents the forces from moving the clamp. A circular clamp will not be in that condition except within two small arcs of it's circumference. I don't think it will stay tightened as well.

http://ixian.ca/pics6/cam2.gif

lazlo
07-02-2009, 01:19 PM
Here's the second pic for the cdcotools system.
http://cdcotools.com/morepics.php?itemid=477

That's a picture of how the Mitee-Bite clamps work :) The cap screw is eccentric, not the hex nut.

Michael Moore
07-02-2009, 02:19 PM
Evan, I like your cams. They might also lend themselves to use in a part where you could mill some slots in the side of the work so the cam could be inserted into the slot and when tightened down to the t-nut, also hold the part down as well as putting the side clamping force into the part. I've found that with the M-B clamps you've got to watch that you don't pull the part up off the table.

cheers,
Michael

gnm109
07-02-2009, 02:23 PM
Decided to make some eccentric clamps to match der operator.

Got a job in from a well know aero engine maker who wishes to remain anonymous but has RR in the name.

Three bars with pegs to go into holes that act like a simple 3 jaw chuck to hold a turbine blade in the crack detection tank, nothing critical, no flight safety crap and you can put any non ferrous metal into these tanks.

However this anonymous company decided they need these bars making out of 30shïtfacedrockhardtoolcrunchy stainless steel.

Unfortunately this grade is only sold in sheared strip and not cold rolled with the result that [a] it's not flat, [b] the edges are rounded where it's been sheared and [c] it's the most terrible material known to man or beast and [d] it's not magnetic.

So they want the bottom face machined flat, all over.
No good clamping to the bed and doing it is stages as when the claps are released it will still be bent, soooooo I need to hold it by the edges whilst I mill the whole side in one go.

Now I have seen these Mighty Bite clamps before in pictures but never in the flesh, looked them up in MSC J&L and had to lean on the battery charger to get some resuscitation back into the circuit, [ damn Lucas pacemakers ]

Seventy freaking nine pounds each ????????????????? leastways I think each as there is no picture.

Soooooooooo, raid the scrap box and mill 4 long tee nuts, tap for one Allen screw and one grub screw. Bit one done

Lob a chunk of 22mm bar [ 7/8" to the metrically impaired ] in the chuck with three bits of banding under one jaw to throw it off centre, drill and ream to 5/8" to fit head of 10mm Allen screw, loctite and whack onto head of screw with large bopper. Bit two done.

Find long U bolt nut off 32 tonne trailer, bore 22mm and part off 4 pieces. Bit 3 done.

All bits present and correct on duty.

http://www.stevenson-engineers.co.uk/files/eccentric_clamp1.jpg

Did some spare Tee nuts at the same time.

Shot of the setup.

http://www.stevenson-engineers.co.uk/files/eccentric_clamp2.jpg

Three fixed fingers at the rear, eccentric clamps at the front with some normal tee nuts to act as spacers and be lower than the top face.

http://www.stevenson-engineers.co.uk/files/eccentric_clamp3.jpg

Close up of the clamp, you place the clamp, nip the grub screw to hold the tee nut into position then wind the Allen screw round and the eccentric forces the hexagon piece against the work.

Doesn't need to be hexagon, could be square the main bit is the eccentric action.

.


Sir John, I thankee mightily for the pictures. I shall save this here thread and when I get underway shortly with my new to me Mill, I'll be making some of those eccentrics. Very nice technical exposition, I must say.

Regards.

Davidhcnc
07-02-2009, 06:57 PM
Mine is a bit more simple and suits a particular job I do often.

The wedge is knocked(brass drift) or levered up.

http://homepage.ntlworld.com/david.hull35/Other%20Images/wedge%20clamp.jpg

http://homepage.ntlworld.com/david.hull35/Other%20Images/wedge%20clmp.jpg

John Stevenson
07-02-2009, 07:08 PM
Made an eccentric 'cam' up tonight like Evans, I say cam because as this was a rush job it was a hole bored in a disk off centre.

Drilled it for the pin holes on a large angle grinder spanner to get some purchase and bolted down. I put a bit of 5/32 bronze rod inbetween the 1-2-3 bolck and the cam, the idea was to measure the indent as a comparison.

Just this simple 'cam' worked well and reduced the bronze rod by 10 thou so it does nip.

http://www.stevenson-engineers.co.uk/files/eccentric_clamp4.jpg

Now the mod I made was to bore the centre hole out tapered, in this case 15 degrees per side, no reasoning behind it, just looked a useful taper.

http://www.stevenson-engineers.co.uk/files/eccentric_clamp6.jpg

Typical rough arsed 4 jaw chuck, achieved by setting one jaw of a 3 jaw over with a packer.
Ignore the slit and hole in the edge, these are the scrap pieces out of laser cut plates that come in handy for washers and other bits.
Hole has been bore to the taper and the large diameter is equal to the head of the 10mm Allen screw.

The screw also has the same taper.

Now without altering anything from setup one the screw is undone and the spanner is used to tighten the plate as before but because the taper isn't seated the spanner has travelled furthur.

http://www.stevenson-engineers.co.uk/files/eccentric_clamp5.jpg


Now once the nut is tightened down if forces the cam outwards because of the taper and leaves a nice big flat on the bronze rod, proof that the forces have been increased.

In fact for anyone wanting to make these can I advise that you get them hardened because after two uses the tapered hole in the cam was showing signs of scuffing badly.

.

JCHannum
07-02-2009, 09:13 PM
I don't quite grasp the tapered hole, but the rest of the concept is understandable.

Mitee-Bites are OK, but overpriced. I don't really see any advantage for them over toe clamps on an application such as yours. Another favorite of mine are the hold downs by Starrett and others for thin pieces. The advantage of both of these over M-B's is that they force the work down against the table while the M-B appears to do nothing to prevent the part from lifting.

TGTool
07-02-2009, 11:48 PM
Maybe I'm just imagining this since I haven't actually handled the Mitee-Bite units, but I thought the screw socket was a counterbore for the eccentric head and the hex was spring loaded between it and the T-nut. This was so that the screw lead would provide a pull down as the eccentric was cramming the work. Dunno now where I got that idea.

I've got a shop made set of the thin hold downs that are a wonderful assist in those situations with thin stock that needs to be held down as well as clamped. IIRC these were just case hardened mild steel, but ground for parallelism and the angle on the backside.

A.K. Boomer
07-03-2009, 12:14 AM
Not at all. I'll be interested to see what you come up with.

To save you some time here is a DXF of the cam profile:

http://ixian.ca/server/camclamp_profile.dxf




Did I miss a chapter in HSM? damn, its good to see you two kids getting along...

lazlo
07-03-2009, 02:02 AM
Maybe I'm just imagining this since I haven't actually handled the Mitee-Bite units, but I thought the screw socket was a counterbore for the eccentric head and the hex was spring loaded between it and the T-nut.

The real Mitee-Bites are just an eccentric socket cap screw in a bronze hex washer. No springs.

They grip really well, especially odd-shaped parts like this cast iron quill stop. Notice that I had to hold the piece down with a conventional strap clamp: cam-action clamps don't resist lifting forces well:

http://i164.photobucket.com/albums/u15/rtgeorge_album/ABHardface009s.jpg


Mitee-Bites are OK, but overpriced. I don't really see any advantage for them over toe clamps on an application such as yours.

Agreed for the most part, although Mitee-Bites can also clamp curved interior pieces like that quill stop that would be tough with a toe clamp. I also have Mitee-Bite toe clamps, which use the came eccentric cam to clamp, and they do have greater holding power, especially resisting lifting force, but they need a lot more Z clearance:

http://www.miteebite.com/images/product_pages/t-slot_toe_clamp_1.jpg

Evan
07-03-2009, 02:16 AM
In fact for anyone wanting to make these can I advise that you get them hardened because after two uses the tapered hole in the cam was showing signs of scuffing badly.



That is why I use a flush socket head cap screw. It has the same action but doesn't bugger up the countersink in the clamp.

.RC.
07-03-2009, 03:07 AM
damn, its good to see you two kids getting along...

That was just a lovers tiff... :D:D

John Stevenson
07-03-2009, 07:58 AM
That is why I use a flush socket head cap screw. It has the same action but doesn't bugger up the countersink in the clamp.

Evan,
This wasn't a countersink but a shallow angle taper.
The idea was to see if the taper action could increase the clamping forces which it did with ease.

It's the same idea that carpenters have used for centuries where they drill dowel hole to purposely be off line so the dowel when hammered in will pull the two parts together.

I thought if it's good enough for Jesus it's good enough for me, lets face it we both operate out of a stable.


I'm not suggesting that everyone make their clamps this way, it's just another variation on a theme.

I do have a few sets of the low hight hold downs but these need three T nuts in a row to fasten, OK for clamping parallel to the tee slots but not in the orientation I was using.

.

Evan
07-03-2009, 09:27 AM
I understand what you are trying to accomplish as the steeper angle will increase the amount of force exerted by the centering action. What you can do is turn the same taper on the cap screw head. Of course that means keeping track of the bolt. If it were I it would mean turning a new one every time I needed it so I used a countersunk screw....

John Stevenson
07-03-2009, 10:22 AM
I understand what you are trying to accomplish as the steeper angle will increase the amount of force exerted by the centering action. What you can do is turn the same taper on the cap screw head. Of course that means keeping track of the bolt. If it were I it would mean turning a new one every time I needed it so I used a countersunk screw....

From my post:-

Typical rough arsed 4 jaw chuck, achieved by setting one jaw of a 3 jaw over with a packer.
Ignore the slit and hole in the edge, these are the scrap pieces out of laser cut plates that come in handy for washers and other bits.
Hole has been bore to the taper and the large diameter is equal to the head of the 10mm Allen screw.

The screw also has the same taper.

.

Evan
07-03-2009, 10:26 AM
Missed that. I recommend hardening the cam... :D

Swarf&Sparks
07-03-2009, 12:06 PM
Here's a quick and dirty variation I use on the router, dunno how it would go with mill forces.
I just use a hefty washer with a hole a bit larger than the shank of a shcs. (my router bed is drilled and tapped M6 on a 25MM grid)
A small washer under the big one allows the bigger washer to pivot as you tighten.
For a quick fix jig, use skate bearings. You can slide stock sizes in and out easily, just use an end stop to hold.

Lets say you're clamping the front of the job against a fixed backstop. Push the washer to the left and up against the workpiece as you tighten the screw. It will "cam" quite tightly against the job.

Tightly enough for 1/2" bit cuts in jarrah. (look it up, eucalyptus marginata, latin for "bloody hard")

John Stevenson
07-03-2009, 12:23 PM
Missed that. I recommend hardening the cam... :D

Never thought of that :D :D

Evan
07-03-2009, 12:53 PM
One can never own too many clamps. It's an axiom of tool use in general.

http://metalshopborealis.ca/pics2/shapsup2.jpg

Paul Alciatore
07-03-2009, 02:29 PM
Nifty concept Evan.

For those of us sans CNC, it looks like a slice of round stock with a hole drilled off center could substitute for the cam. Leaves room for extra spanner holes giving more options for the handle angle while securing.

John



I haven't tried it but I don't think a circular cam will work as well. I designed the spiral cam to have the clamping force vector pass through the bolt hole at all angles of rotation. This prevents the forces from moving the clamp. A circular clamp will not be in that condition except within two small arcs of it's circumference. I don't think it will stay tightened as well.

http://ixian.ca/pics6/cam2.gif


Evan,

The forces on your clamp may pass through the bolt hole, but not through the center of the bolt. Assuming that the clamping force is normal (perpendicular) to the clamp surface, the radial lines on your drawing are not the force vectors because these radial lines are perpendicular to the straight lines at their ends, not to the curved, spiral edge of the clamp.

I am sure you know this and that is why you did not claim that the force is directed to the center of the bolt. But this offset will cause a slight unbalance in the forces and will tend to loosen or tighten the bolt depending on which way the clamp's spiral is oriented.

What I do take exception to is your claim that your spiral is superior to a circular segment with an offset hole. A circular segment with an offset hole will have the clamping force directed through the center of the screw at two positions that are 180 degrees apart. Between these two positions it will vary from very small when near these positions to a maximum at a point half way between them. In contrast, your design appears to have a certain amount of offset at all points. So, with careful design, the circular design may be just as good or perhaps even better.

To keep the forces directed within the bolt hole for the circular design, you should make the offest of the hole less than the radius of that hole. With a 1/2" bolt hole that would be less than 1/4". A 0.125" offset would give a 0.250" tightening range which should be good for most situations. If you design your setup for first contact at mid range, then you will be decreasing the offset as you actually tighten the clamp. And a round clamp can be tightened in either direction: CW tightening would be the direction to use to have the clamping force tend to tighten the bolt.

Actually, with a circular clamp, you could plan on using this effect to help keep the bolt tight. You could drill the hole at a greater offset and always tighten it in the CW direction. With an offset that is beyond the bolt hole, the tendency to tighten the bolt should be even more. But I wouldn't go too far as the mechanical advantage and hence the clamping force, will be less.

And no CNC is needed.

small.planes
07-03-2009, 04:18 PM
http://metalshopborealis.ca/pics2/shapsup2.jpg

I dont think that ones gettin away Pa :D :p

Dave

clutch
07-03-2009, 07:46 PM
One can never own too many clamps. It's an axiom of tool use in general.

http://metalshopborealis.ca/pics2/shapsup2.jpg

Don't ever show that picture to a woodworker.



I do agree that you can't own too many clamps.

Clutch

Evan
07-04-2009, 01:33 PM
If I am not mistaken those are Clutch'es clamps.

Glenn Wegman
07-04-2009, 01:41 PM
If you want something that will really hold and create down force on the part use "edge clamps". Available in different sizes and configurations.

http://img.photobucket.com/albums/v647/Fighter1/Edge.jpg

lazlo
07-04-2009, 01:52 PM
If you want something that will really hold and create down force on the part use "edge clamps". Available in different sizes and configurations.

Those are what Jim and I were calling "toe clamps."

Glenn Wegman
07-04-2009, 02:18 PM
Lazlo,

These are different then the Mighty Bite toe clamps that I believe you were referring to. The Mighty Bite toe clamps still use an eccentric. On these the nose piece slides on "ways" on a 45° angle and is done so by a "leadscrew".

Glenn

BadDog
07-04-2009, 04:34 PM
I've got some of those shown by Glen. They really work amazingly well, well enough to mark material at times. But they are taller, sometimes too tall, and mine have some cutter strikes to prove it...

dp
07-04-2009, 07:28 PM
Nice Tiffie, Pity I didn't have three weeks to wait whist they shipped as for $22 it's not worth the time to make.

Is it me or the pic but it looks like theirs have the eccentric screw tapped on the piss ?

.

I think they're plumb but one hex ring right rear in the picture has hooked a thread on the grub giving it an off-plumb look.

JCHannum
07-04-2009, 09:47 PM
If you want something that will really hold and create down force on the part use "edge clamps". Available in different sizes and configurations.

http://img.photobucket.com/albums/v647/Fighter1/Edge.jpg

This is what I refer to as a toe clamp. This one is 1-1/4" wide. The jaw is only 1/4" high so it does not interfere with much. They will hold until Hell won't have it and they draw the work down flat to the table. They are hard to beat.

http://i320.photobucket.com/albums/nn351/jchannum/P1070071.jpg

If thinner work is to be held, I use hold downs in the vise.