[project5k]

I'm working on a product, that, if all goes well, i will need to be turning out multiple units as quickly as i can. I have a couple questions about fixturing, and how i can make my production process the easiest.

What i will be making will start out as a cookie, or slug, cut off of t-6061 alum, 2.5 inches in diameter, and about .750" thick.

My thinking was to take a couple of the larger "tooling plates" that i have that are all alum, and bore some countersinks into it, drill a hole through the center, and put a rubber "O" ring down inside, and through the hole in the middle of the depression, i would attach a suction, or vacuum pump of some kind, to hold the slug in place during machining.

I will need full access to the top and the upper .250 of the slug, so side clamps are out.

My thinking is that i would have multiple depressions, and thus could machine multiple parts in one pass, then, have a second set of depressions, that i could then flip the cookies over in, to machine the backsides.

My questions are as follows.

What should i use as a gasket material in the depressions, to make a seal between the cookies, and the fixture?

What can i use to make the vacuum? obviously a shop vac isnt really gonna work in this case, just not enough surface area to work on, so i'm thinking its going to have to me a fairly decent vac source.

and since i'm running full flood coolant, what do i do about any coolant that may get sucked into the vac ports, do i just have an accumulator of sorts, so that the fluid gets collected before the pump?

I was wondering if i could use something like the harbor freight vacuum pumps, but i didnt know if anyone had one, every tried what i'm doing, or had any idea if it would work...

i tried searching for some of this stuff, but everything i searched for came back, "no matches found"

I'm looking for any input, ideas, thoughts, and so forth, if anyone has done anything similar to what i'm talking aobut, and you have pictures, i sure would love to see them...

[Geof]

I doubt you will get enough holding power.

2.5" diameter is 4.91 square inches.

Full vacuum, which is not possible, is 14.7 pounds per square inch.

You will have less than 72 pounds holding your part down, it will certainly spin and very likely will lift out under the force of the cutter.

Side clamps are not out, you have 0.5" of space to clamp on the side; top clamps are out.

Do you have a decent sized vise? Make yourself some custom jaws with a 2.5" diameter hole about 0.45" deep and you will have plenty of holding power.

EDIT:

When you want to scale up for high volume start another thread and I will suggest how you can make a multiple holder using air clamping.

[JimPAC]

You'll spin your wheels trying to get a vacuum to work and it wont!
Geof has the solution"

[escott76]

I'm working on a product, that, if all goes well, i will need to be turning out multiple units as quickly as i can. I have a couple questions about fixturing, and how i can make my production process the easiest.

What i will be making will start out as a cookie, or slug, cut off of t-6061 alum, 2.5 inches in diameter, and about .750" thick.

My thinking was to take a couple of the larger "tooling plates" that i have that are all alum, and bore some countersinks into it, drill a hole through the center, and put a rubber "O" ring down inside, and through the hole in the middle of the depression, i would attach a suction, or vacuum pump of some kind, to hold the slug in place during machining.

I will need full access to the top and the upper .250 of the slug, so side clamps are out.

My thinking is that i would have multiple depressions, and thus could machine multiple parts in one pass, then, have a second set of depressions, that i could then flip the cookies over in, to machine the backsides.

My questions are as follows.

What should i use as a gasket material in the depressions, to make a seal between the cookies, and the fixture?

What can i use to make the vacuum? obviously a shop vac isnt really gonna work in this case, just not enough surface area to work on, so i'm thinking its going to have to me a fairly decent vac source.

and since i'm running full flood coolant, what do i do about any coolant that may get sucked into the vac ports, do i just have an accumulator of sorts, so that the fluid gets collected before the pump?

I was wondering if i could use something like the harbor freight vacuum pumps, but i didnt know if anyone had one, every tried what i'm doing, or had any idea if it would work...

i tried searching for some of this stuff, but everything i searched for came back, "no matches found"

I'm looking for any input, ideas, thoughts, and so forth, if anyone has done anything similar to what i'm talking aobut, and you have pictures, i sure would love to see them...

As the other poster said, soft jaws. Make a copy of your vise jaws in aluminum. Cut them so you get a piece of the radius in each one. You don't need a complete circle in the jaws, just make sure they are closed on something when you cut the jaws. Even .25" of depth in the jaws will do a whole lot. At work I use soft jaws almost exclusively. It also makes setting your offset easy, as unless you unbolt them from the vise they will always be in the same place.
There are other kinds of fixtures you could make. There are low profile side clamps that use cam action. You'd want a pair of fixed blocks to center the blank against though.

[project5k]

ok, i had wondered if the vac would be strong enough, guess that confirms my fears that it wouldnt be...

So, if i'm gonna go the route of making half moon clamps, (vice jaws) then i could use compressed air and some short throw, medium to large diameter(I'm thinking 1 inch) air cyls and just do it that way.. i have 185psi compressed air on tap at all times...

another plus of going that route is i dont have to worrie about coolant inside of vacuum pumps and all that jaz.

[Geof]

..So, if i'm gonna go the route of making half moon clamps, (vice jaws) then i could use compressed air and some short throw, medium to large diameter(I'm thinking 1 inch) air cyls and just do it that way.. i have 185psi compressed air on tap at all times...

185psi air, that is high!!! But not high enough.

A 1" diameter cylinder will give you about 145 pounds of force closing your air vise, not enough I am afraid. You would need something like a 3" or 4" diameter cylinder.

If you do not have a vise make yourself some halfmoon clamps that are closed using a couple of bolts, just like a split clamp except one half is machined into your plate.

[project5k]

hmm thats an interesting thought.. so tell me, do you really think i need over 2000 lbs of clamping force? a 4" cyl * 185 psi = 2323.6 lbs of force.. wow, sounds like i'm really gonna be crushing these things..

or is my math wrong? area of a circle is pi*r^2
3.14 * 2^2 = 12.56in^2
12.56 * Air pressure, 185 = 2323.6

now i know that there are some losses, and i know that my compressor comes on at 180 and turns off at 195 (according to multiple unrelated gauges)

but for your example on the 1" cyl, i get 3.14*1^2*185=580.9lbs of force.

where am i going wrong on the math?

[escott76]

hmm thats an interesting thought.. so tell me, do you really think i need over 2000 lbs of clamping force? a 4" cyl * 185 psi = 2323.6 lbs of force.. wow, sounds like i'm really gonna be crushing these things..

or is my math wrong? area of a circle is pi*r^2
3.14 * 2^2 = 12.56in^2
12.56 * Air pressure, 185 = 2323.6

now i know that there are some losses, and i know that my compressor comes on at 180 and turns off at 195 (according to multiple unrelated gauges)

but for your example on the 1" cyl, i get 3.14*1^2*185=580.9lbs of force.

where am i going wrong on the math?

R not D. .5x.5xpi

[project5k]

please explain further. a 4" diameter cyl would have a radius of 2", 2^2 or 2 squared is 4. 3.14 times 4 = 12.56

the formula is pi times r squared, right? thats the area of the circle, or piston, then multiply that times the air pressure to get the output force?

[SCzEngrgGroup]

please explain further. a 4" diameter cyl would have a radius of 2", 2^2 or 2 squared is 4. 3.14 times 4 = 12.56

the formula is pi times r squared, right? thats the area of the circle, or piston, then multiply that times the air pressure to get the output force?

You can use a smaller cylinder if you provide a lever or cam to give mechanical advantage. A 1" cylinder with a 16:1 lever will give the same clamping force as a 4" cylinder with 1:1 lever, and you shouldn't need much travel on the workpiece end, so even a 1" travel cylinder should work. You could also use a hydraulic cylinder instead of a pneumetic one, and run MUCH higher pressures (like > 1000 PSI).

Regards,
Ray L.

[Geof]

I always like to err on the side of holding things too tight rather than too loose but notice I did give you a range; 3" for about 1300 lbs and 4" for about 2300 lbs.

The lever suggestion is also very viable and you can also get force multiplication by using a toggle clamp or a sliding wedge. These are more complicated to build but when your volumes increase it becomes worthwhile putting in the extra effort on the fixturing to reduce the reloading time.

An advantage with both the toggle clamp and wedge is that they can be self locking so if you lose air pressure you do not get parts flying around. In this case you need a double acting cylinder because force is necessary to unlock.

[escott76]

please explain further. a 4" diameter cyl would have a radius of 2", 2^2 or 2 squared is 4. 3.14 times 4 = 12.56

the formula is pi times r squared, right? thats the area of the circle, or piston, then multiply that times the air pressure to get the output force?

yes, but where you calced the area of a 1" cylinder you used 1" for the radius, and it's .5"
.5"*.5" = .25"
.25"*3.14*air PSI = 145

[BobWarfield]

Check out Mitee Bite clamps to clamp by the edge. There are some cheap clones of those floating around that are available from places like Shars.

Best,

BW

PS The clamping force issue is an interesting one. Very hard to find recommendations on that if you go searching. Carr Lane is one source. I was surprised by how little force they show as optimal for a step block clamping setup. Their issue was not to approach the failure point of the studs too closely. Their recommended torque on the bolts was WAY less than anyone I've ever seen tighten down anything on a mill table. LOL!

[mc-motorsports]

or use a lathe chuck clamped to the milling table, machine up some soft jaws, self centering, pleanty of holding power. I do it all the time. Last job was starting off as 2" diameter 52100, didn't budge a bit.

Multiple lathe chucks is your multiple fixtures. Use your G54-59 offsets for each chuck.

And a 3 jaw scroll chuck eliminates the problems with round soft jaws on a milling vice, including centering. For instance, if your OD is +-.005, but your milling opps require .002" concentric, your part center is going to move around.

[project5k]

ok, .5 vs 1 on the radius, got it, i see my mistake on that one.. and true you did give a range..

i was thinking about the cam/lever mechanical advantage idea, i have a couple cyl's that i could use, thier 1.125 piston diameter, and i do like the idea of having it setup so that if i were to loose air, i dont loose my part, break a cutter, and have to duck really fast.. hehehe, been there done that... not fun.

I dont see the need for hydro strength, first of all i dont have a source(pump) and secondly, if i were to spring a leak, i'd have to deal with hydro fluid in my coolant, i dont like the sounds of that.. I've been using the same coolant for over a year now(just adding water to make up for evap)

where i'm working with t6061 alum, i was wondering if i should consider using some hard plastic on the jaws of the clamp to keep from marring the surface of my part, perhaps something like cutting board material..

I like the simplicity of the lathe chucks, but i only have the ones that are on the lathes now, and that seems far more expensive than using materials i already have to make a more vice like mount... If i use some half circles or even "V" knotches for the parts to go in, i would think that i would get pretty consistant mountings.. fortunately these parts dont have to be ballanced, or rotate in thier end use, so if i'm off my mark by 5 thou then i'm still in good shape...

I've never used offsets that i'm aware of. My plan was to just have enough clamping locations, and then have the one program run all of them in one whack.. my thinking was something like a mini assembly line, the first station or clamp would do the top of the top, then station 2 would do the bottom of the top(the part gets flipped over) Then station 3 would do the top of the bottom part, and then the 4th clamp would do the bottom of the bottom.. I would have 4 parts on the table at any one time, each in different stages of compleetion, then as the parts move from one station to the next, you take the finished parts out, and put in new blanks, and just run the same program over and over, that one program would cut all 4 stations...

In my mind, its easy to draw, easy to program, and since there are no tool changes necessary, it should go pretty smoothly all the way through all 4 stations..

The other thought that i had was to lay out the stations so that each end of an air cyl is working on a clamp, so with 4 stations, i would only need 2 cyl's... the drawing is not to scale or anything, but it'll give you a good idea what i'm thinking... ofcourse this dosent include any kind of a failsafe.. better ideas on how to do that?

course, i guess, considering that i'm probably gonna have about a 1 hour cycle time to do all 4 parts, i guess, sliding hand operated clamps would be the easiest.. and simplest, and simple allways wins over complicated in the long run...

[Geof]

You have it pretty much worked out. Just a few comments:

Vee clamps do not hold as securely as a halfmoon, they can allow twisting because of the small area of contact.

An easy way to get high pressure for hydraulic clamping is to use a multiplier; have a large size air cylinder operating a much smaller hydraulic cylinder. Set it up with a reservoir much like a brake master cylinder so that when the air cylinder retracts it draws fluid into the hydraulic cylinder and allows any air bubbles to escape. Instead of hydraulic fluid or oil use coolant as the workinf fluid and you don't have any problems with leakage.

You multi-station approach is the way to go but see if you can figure out some sort of locating pin system so you cannot put partially finished parts in the wrong station.

[SCzEngrgGroup]

I don't think any kind of plasitc in the clamps is a good idea - it won't hold securely enough. Aluminum clamps should not mar your parts if they're a matching contour and smooth on the contact faces.

You definitely should have the clamps match the contour of the parts, don't just use Vees - they won't hold securely, and the small contact area is far more likely to put flat spots on your parts, or score them (and the clamps) if the parts turn while cutting.

You could actually do four parts with only a single air cylinder, by putting a bar across each part of parts on the left and right of your fixture, and having the cylinder act in the center of that bar. That will ensure equal force on all four clamps, as the extra bars will balance the force applied to each, regardless of any minor dimensional differences.

Regards,
Ray L.

[project5k]

larger cyl operating a smaller one, got it, that makes sence,

on the v shaped clamps, i can see your point, i will machine the half moons....

i never thought about using the coolant as the operating fluid.. thats freakn brilliant.

I follow your idea about the bar and just using one cyl. the only drawback is that i have to have something in each station, or build in some stop pins...

I'm not too worried about getting things in the wrong locations, about the only think i could mess up would be to put a half done top, in the bottom machining stations, but as far as doing each half, dosent matter which side gets done first...

ok, i updated the drawing, i know what you mean, its just really hard for me to draw in paint... if i were at home and had my software, i could definately draw it better..

[SCzEngrgGroup]

larger cyl operating a smaller one, got it, that makes sence,

on the v shaped clamps, i can see your point, i will machine the half moons....

i never thought about using the coolant as the operating fluid.. thats freakn brilliant.

I follow your idea about the bar and just using one cyl. the only drawback is that i have to have something in each station, or build in some stop pins...

I'm not too worried about getting things in the wrong locations, about the only think i could mess up would be to put a half done top, in the bottom machining stations, but as far as doing each half, dosent matter which side gets done first...

ok, i updated the drawing, i know what you mean, its just really hard for me to draw in paint... if i were at home and had my software, i could definately draw it better..

That's still more complicated than it needs to be. The new bars should be solid bars running all the way across each pair of clamps. These bars are completely free-floating. The lever connected to the air cylinder connects to a single pivot in the center of each bar. You can eliminate the extra parts connecting the two in your drawing. The clamps, of course, are also pivoted on the ends of the bars, so they will self-align.

Regards,
Ray L.

[SCzEngrgGroup]

Here's the idea, on the left side of the drawing. (Paint SUCKS!)..

Regards,
Ray L.