Best practice for softjaw fixturing

CAD/CAM/CNC
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I am learning that fixturing is an area I have MUCH to learn. Currently, I keep it simple with soft jaws and they work well enough.

But I’d love to hear from those who use them regularly.

A few questions to start this off:

  1. Do you have a particular way you set your part offset, a hole? an edge of the jaw? Jaw centre?

  2. How do you get repeatability next time you run the same jaws? Do you have a setup sheet, or record the machine co-ordinates? (don’t imagine that would work as you could move the vice…)

  3. what is the best way to go about holding a round part in softjaws?

  4. how do you successfully hold multiple parts in softjaws?

  5. how do you avoid marking the finsihed part when you clamp it in the softjaws for op2?

The only tip I can offer people just setting out, is remember that external corners on your parts, require internal corners on the softjaw, but you can’t ever get a square corner with a round endmill, so BEFORE you machine our the softjaw, drill the corners out, use a drill cycle in fusion, and select the point the two lines meet in the corner as the geometry, set the height to match the bottom of the model (remembering to add enougn to account for the fact your drill has a pointed end, so you may need to go a touch deeper) - then machine out the negitive of the model - it looks a bit funky, but works well.

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  1. Use datum callouts when possible and towards solid jaw or non-moveable surface

  2. If using jaws, skim on side of jaws in clamped state and you can indicate them in less than .001

  3. 1/8 shim/parallel between jaws and pocket out diameter so part just barely fits. The wider the jaws are the more surface covered

  4. Usually only hold two parts per jaw because if there’s any difference in parts then the
    chance of them being pulled out goes up. With two parts, the jaws will pinch uniformly

  5. Use aluminum jaws and clean out every cycle.

My two cents…

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A few things we do:

1- Generally we shoot for the upper left corner of the part. If the part is round we will usually use the center. Complicated parts, will sometimes get centered too, as we will machine soft jaws using the same wcs point.

2- We don’t. We usually skim our jaws .015-.030” each time if we reuse ones that were previously machined for the same job. Aluminum soft jaws can get muddled up, and this can help keep them with nice clean surfaces to grip with. Though there are a couple systems out there designed for repeatability, we have not tried them.

3- Round part = round cutout to match same diameter - usually we cut the diameter .002- .003” under the part diameter being held for aluminum soft jaws. Cut the diameter using the same wcs as you use on the part. perfect every time.

4- This can be tricky. Generally I’d say one on each side of the jaws - and only 2 parts per jaw. But sometimes a parts geometry will allow you to do more, and if it can be held deep enough. Also depends how good the jaws are cut and if you are getting aggressive with machining. Multiple part holding usually means you have a bunch to do, if you have a bunch to make then you are probably going to be getting aggressive. So you need to decide if it’s worth the risk trying to hold more than two per jaw. Throwing a part sucks - inspecting the tool, broken tools, fixing or remachining jaws takes a ton of run time off the clock.

5- Depends, aluminum soft jaws don’t leave too many marks if you keep them clean and in good/crisp condition. Get a chip stuck in it and it’ll mark everything going in it. You can use a piece of paper between the part and jaws. But most of the time you run without. Really depends on what you are trying to accomplish with the part.

We try to keep our jaws in the vices as much as possible and just cut them up for each job, then flip them over and start cutting up the bottom side. If you plan your jobs a little in advance, and don’t cut such deep pockets that the jaw is useless after that job - then you can get alot of life out of them.

How’s that for a first post… :wink:

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wow if these responses are an indicator of how great this group is going to be … then wow !!!
I have nothing to add that was not covered above…

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For us, it depends on if we know we have a repeat job or not. If not, it often isn’t worth the extra time to make the jaws fancy.

If it is not or we do not know if it will be a repeating job, typically the operator will mount the jaws. The pickup will typically be the center of the back jaw for X0, center between the jaws for Y0, and top of the jaws for Z0. They will be instructed to clamp the jaws while spaced a given value apart, and also given the depth of the pocket and size.

Most soft jaws we make are for round parts, so if the jaws are not cut up for another usage, they are relatively easy to align - leave both jaws loose, eyeball the jaws aligned and then clamp a part. You can then tighten the mounting screws and the jaws should be aligned correctly.

If it is a repeat job, we try to make the front jaw more mobile, IE not required to be aligned any certain way with the back jaw, where possible. Typically we will then come off the left edge and front face of the back jaw for XY0, as that is a quicker pickup than center. We use the same pickup to machine the jaw as well.

An alternative to that may be a datum hole, as previously mentioned. I prefer the front/left corner of the back jaw myself, but an interpolated datum hole in the jaw could be more accurate.

My preference for round parts is actually to use hard vee jaws where possible - you have the same time in swapping jaws but you don’t (potentially) burn $10 of jaws and labor every time you need to hold a round part.

But for repeatability and ease of use, cutting a counterbore for the part to sit on is best, especially if there are several parts - no worries about the part not sitting straight in the vee…

If you have a thin ledge on a cylindrical part you can relieve your jaws with a t-slot cutter or similar if there is a more substantial diameter to clamp on.

Holding multiple parts is easy (for round parts) IF you have good process control on your round parts. We have a job coming up, a repeat job, of 220 pins with 8mm diameter stems. With one set of jaws I can hold 6 at a time for the mill up (facing thickness, milling a flat and cutting three counterbored holes). Like any “high-density fixture” it saves a ton of time in tool changes and rapid moves.

For flat parts I don’t really recommend holding multiple parts… at the most, hold one part on the left end and one part on the right end of the vise. And really, it don’t have to be soft jaws for this. Any more and you run a risk of clamping some parts tight and others not. It can be done - but there is an inherent risk.

A well-made soft jaw, blown out correctly, should not mark an aluminum, brass, steel or harder part… plastic might be different. But if you have matching contours, it should make the pressure even around the perimeter.

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Note: this topic was moved into the “CAD/CAM + CNC” category.

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I didn’t read everything listed but could see from the first few comments, that you pretty much got some amazing answers. I will add a few little things that may go above and beyond the basics…

  1. I also use a 1/8 parallel as a spacer and usually just choose a size that allows it to sit just below pocket or cut out being machined.

  2. We usually use 1 x 2 6061-T6 Alum Bar as a standard size and cut blanks to 8.0 inches… sometimes longer, sometimes shorter depending on custom needs.

  3. We face the back of the softjaw, meaning the side that touches the vise, so the fit is perfect… and face the bottom of the jaw also, which also touches the vise. These 2 faces should be at a perfect 90 degree. This process allows us to take the jaws out and put them back in.

  4. Be careful with the Hammer… If your putting jaws in many people use a hammer to slam them down. I don’t as the vibration can easily lift the jaw instead. If you have cleaned the vise and skimmed your jaws perfectly, the fit should be precision. I would put the jaws in place… lock them down just snug / light … and then tap with the hammer, very carefully to ensure the jaws sit on the vise perfectly and that when you lock them in harder with the bolt, they don’t move… It’s precision… so treat it as such.

  5. Once the jaws are locked, loaded and cut to the final shape… its a good idea to close them and run a endmill along the left outside edge… This will allow you a way to indicate them both together, when you replace them at a later date.

  6. A tooling Hole - I often have my guys place a .2500 perfect hole on the softjaw that is attached to the hard / dead vise. Meaning the side that stays put and does not ever move. This hole is a locating hole… so you simply document the location compared to you XY 0 and then when you put the jaws back in at a later date… You can simply indicate the .2500 hole and move over to find your perfect XY

  7. When machining precision parts that have tight tolerances. You should try to cut the pocket to hold the part, deeper than the carrier jaws. Meaning… The vise is 1.5 high… The soft jaw is 2. high…

If the bottom of the part is sitting at 1.7 high, because you cut the jaws Z-.3 deep… you could have a issue…

Because the power of the vise is coming together below from the bottom “0” to 1.5 high since that’s the height of the vise. So if nothing is there because your part is high, then the power will cause the jaws to V out or deflect since the jaws are only hitting the part. Make sense? So, added pressure will make it so the part is only being held at one point at the bottom of the part and not on the sides of the part because of the flair out.

So, I recommend to cut the jaws down and cut the pocket below the height of the vise… so the vise pushes straight into the part and keeps all surfaces parallel and perfect.

  1. I usually cut pockets to the exact shape of the part, adding clearances as needed. When cutting the pocket, I always notice that my Y zero will move slightly towards the dead jaw. Understanding this and compensating for it can help you make a perfect part the first time around. This happens because the moving jaw pushes the part to the dead jaw… So usually, if my XY zero is center… I will offset the Y .002 approx… and then double check it if possible by checking off the back jaw if it’s straight or facing the back off excess material on op#2 if that’s the case and indicating a known / perfect feature.
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So, you install the soft jaws, machine/drill/ream the hole, make note of the precise location of the hole. The next go around with those soft jaws, you indicate your spindle to the center on the hole, then set your xy0 to the appropriate values as noted when the hole was positioned in the first place.

Did i understand that correctly?

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You got it for the most part but Titan had a lot more Info you might study his comment some more.

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@AndrewGiles If you make a lot of soft jaws and are looking for repeatability check out these dovetail quick change vise jaws http://carvesmart.com

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I think you got it…

Let’s say I have a real odd shape like a letter “S” meaning the part looks like a S.

I would Machine my jaws with my XY 0 in the up/left which potentially isn’t touching the part at all… and could never be edge found.

If there was space at that location I could drill a precision hole… and call it XY zero
And indicate it, the next time.

If not I could just pick any spot from G55 XY 0
Like X-.5 Y .375 and out a Hole.

Then the next time,
I would I indicate my spindle to the hole… and move X.5 Y-.375 and then RE-Zero G54 Right There.

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I have typically made mine similar to the other guys, however with a job that may require the jaws to be reused, I have added dowels in the faces of the jaws also to guarantee the jaws are located side to side in the correct position. I also tend to try to create a stackup of gauge blocks so the vise is at the open distance it will be with the part in it… not sure that it matters much as long as the vise is clamped on something, but it has worked well for me.

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I couldn’t agree more! I do take another approach with the same twist. On double vises, Chick, Orange, etc. I actually do my hole in the center of the hard jaw, and then when programming, base every work coordinate off of that hole. That way when I take jaws in and out, and vises in and out, I only have to dial in on the center of that hole, and my vise and every job is dialed in. Dialing in a hole is quick and easy, and saves even more time by having that common point on everything. This works great because of CarveSmart Jaws!

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I remember not very long ago how confused I was on making soft jaws, now i’m whipping them out left and right. But here is the process I’ve been using and wondering if I could be doing better.

  1. insert jaws into my model assembly (each jaw has to be a separate part, named differently) at a distance apart that I can use a parallel in the vise to separate the jaws for machining the pocket.
  2. Cut the profile of part into the jaw .001" larger all the way around (.001 has been working good for me, should I change this to a different dimension?).
  3. Set my G54 or whatever to the top left front corner of dead jaw.
  4. Program my cuts in the soft jaws.
  5. Program my 2nd Op of part using the same G54 as I used in my soft jaw program making sure to add clearance for the top of the part so I don’t have a crash.
  6. Machine all 4 sides of 1 x 2 bar stock to what I need.
  7. Mount Jaws into vise.
  8. Set my G54 to the top front left corner of the dead jaw.
  9. Machine pocket in soft jaws.
  10. Make parts.

Since i’m still wet behind the ears, Can I be doing this process better and more efficiently?

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Exactly - That’s the cool thing about this trade… once you get it, then you simply go through your library of techniques and tools and figure out what works best for any given set up.

I simply just stated a few things that came to mind with the minutes I had.

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You are completely right on that. What is best practice for your setup may not meet someone else’s needs. We have so many amazing options, and individuals that can help us get to the finish line, but ultimately we have to do what is going to work best for our situations. Sometimes that will come from copying what someone suggests, sometimes it comes from a completely different solution. What is great about this forum is that you can get advise, give advise, and bounce ideas off of others to help you get it done!

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