Work Holding - vises and such

[gadget_lover]

It seems that work holding while machining is a craft unto itself.

The big boys use collets and clamps and special vises, while us newbies use whatever we can find (vise grips through bench vises)

So I've bought the step blocks and I have the machinist vises and the hold down clamps with studs and T-nuts. I even bought a screwless vise for precision work.

But I realize that I don't really know how secure things need to be. I've held things by hand while feeding them into a spinning end mill and watched it go flying. I've clamped things so tight that I've deformed them. I've used 1, 2, 3 and 4 clamps to make sure my work would not budge.

Now I'm talking about a micro mill with a small table, about 9x6 inches. I only use up to 1/2 inch end mills, so it's not hogging out big chunks.

So what are the general guidelines people use when clamping / securing a piece for milling?

BTW, I'm still wondering what the extra bar in this photo is used for. It's just long enough to go from side to side. There's already a similar (but shorter) bar under the vise to secure the jaws.

Daniel

 

[McGizmo]

Re: Work Holding - vices and such

Hummmmm...... It looks like that dowel would go in the hole on the side of the fixed portion of the vise? I wonder if it's for referencing or possibly clamping the vise to the table? /ubbthreads/images/graemlins/icon3.gif Good Q! I have a vice similar and use it all the time. It's a PITA to adjust but it does give great and parallel clamping when set properly! If only set up on a mill were as easy as chucking a part in a lathe! /ubbthreads/images/graemlins/grin.gif

 

[tvodrd]

Re: Work Holding - vices and such

How hard to lean on a vise handle is something only gained by experience. (Speaking for my own case.) I suspect most of us get very paranoid at a very early stage after the first part gets sucked out of the jaws and breaks a cutter or worse.

A cheepie mill vise can be a real PITA trying to hold work to any accuracy. They usually get sprung from over tightening, which causes the jaws to push the work piece upwards when tightened. A candy axe (plastic hammer) helps to beat the part back down when tightening. Good vises like Kurt Angle-Loc (and good copies) are designed to cam the moving jaw downwards as they are tightened and really help. Dull cutters in the mill will require heavier clamping forces.

How hard to tighten? You'll get a feel for it, and it isn't as hard as you think. (Pun intended /ubbthreads/images/graemlins/smile.gif )

Larry

 

[Guter]

Re: Work Holding - vices and such

The longer pin, pictured to the side of the vice is used in the same way as the pin that is already "under" your vise. The shorter pin is handy for quick adjustment of the moving jaw. The longer pin would be used when you were making multiple parts of the same size, to keep the pin from constantly dropping out of the notches underneath each time you re-clamp.

As far as general workholding techniques. The best overall approach, is to always hold on as much of the part as possible. This means that the best method to hold onto a flat part, is with flat jaws in a conventional milling vise. And with round parts, this means generally holding in a round collet. There are of course variations. Flat parts are usually easier to get away holding in a milling vise, but for round parts in a vise, the key is maximum encapsulation. This is where you really need a collet to hold onto them. If you are just milling you can get a collet block, or alternately get "Soft" jaws for a milling vise, you can mill or bore these in a profile of whatever part you want to mill. This would ensure greater encapsulation, though does get expensive.

Keep in mind that with a precision screwless vise, the best hold you can get on a round part is 3 points. One point is the flat surface of the non-moving jaw, and the 2 sharp points of the "V" in the moving jaw. Unless the material you intend to machine is harder than the vise, you will almost always come out marking the part.

I cannot stress enough how important maximum encapsulation is. /ubbthreads/images/graemlins/icon15.gif

Since you already have your vices, you should be fine for holding flat parts. The best thing I can suggest, for round parts, is that you get a collet block, and corresponding 5C collet set. You can clamp it directly to your mill's table, or hold it in one of your vices, vertically, or horizontally.

Good luck, and hope my first post after trolling for the last year helps. /ubbthreads/images/graemlins/grin.gif

 

[Anglepoise]

Re: Work Holding - vices and such

I have been a machinist ( amateur ) for the last 20 years.
Many times we find ourselves in a situation where the part being held is not 100%.

I have found that if one takes a really fine cut, it is amazing just how delicate the grip on the part to be machined, can be.

However we don't always practice what we preach and after a few minutes removing 5 thou at a time, we all get impatient and turn up the heat. Thats where things go wrong.

Small cuts and lots of patience is the best route.

 

[tvodrd]

Re: Work Holding - vices and such

Welcome to CPF Guter! There are a bunch of DIY guys here that need all the help they can get. /ubbthreads/images/graemlins/icon15.gif "Encapsulate"- I have used Devcon 5-minute on occasion, and I'm not really a machinist! Anglepoise, /ubbthreads/images/graemlins/thumbsup.gif and I concur! Impatience has cost me several flashlights! /ubbthreads/images/graemlins/icon15.gif

Larry

 

[McGizmo]

Re: Work Holding - vices and such

Gutter,
Welcome and thanks for chiming in! Now I need to see if I can find a pin and if my vice will accept another pin below the one used with the tightening screw! "It" drops out at the most inopertune times! /ubbthreads/images/graemlins/icon15.gif

 

[gadget_lover]

Re: Work Holding - vices and such

Now that you've mentioned it, I can see using the extra pin as a way to stop the other pin from rotating or moving to the next slot.

I can't take a picture this week, but the vice jaw has a setscrew that extends through the body to the underside where it's attached to a rod that's at a 90 degree angle. The rod seats into grooves on the bottom, providing leverage to move the jaws. Pretty clever, actually.

Daniel

 

[rwolff]

Re: Work Holding - vices and such

Reading from bottom to top, I hit the "mini-mills" thread first, so my answer to this issue is there - you use either the short dowel or the long dowel.

I assume you're going to be doing some milling. Two things you need to watch out for are:
1. The spindle has to be perpendicular to the table (unless the job you're doing needs it to be at a particular angle). Use a trammel bar and your dial indicator (mill turned off) to check this - when making a full rotation of the spindle (easiest if you put the mill in neutral - between high and low range), the indicator needle comes up to the same number whenever it hits the ground surface of the table (naturally, it'll take a different reading when the point falls into the clamping slots).

2. The vise jaws must be parallel to one of the feed axes (usually "X" - right-to-left), unless you deliberately set them to a specific angle. The dial indicator is your friend here too - when you move the table the width of the vise jaws (of course, the vise is clamped to the table), an indicator mounted in the spindle and with its point resting on the fixed jaw of the vise shows no change in movement.

 

[gadget_lover]

Re: Work Holding - vices and such

Thanks for the info on the vise.

I've used both a dial indicator and a test indicator to check the vise alignment. The test indicator in the chuck (motor off) and the dial indicator attached to a magnetic base stuck to the mills column.

Daniel

 

[cy]

Re: Work Holding - vices and such

Welcome to cpf Guter and thanks for chiming in everyone.

amateur machinist like me need all the help they can get /ubbthreads/images/graemlins/grin.gif

 

[gadget_lover]

Re: Work Holding - vices and such

I was using this vice this week and found at least one good use for the longer bar. The .375 inch rod I was holding left the clamping mechanism right at the edge of the slot that catches it. I'd set it up, start tightening and the mechanism would jump to the next slot.

So I simply set it up again (about 5 more times) and finally realized the meachanism would stay in the right slot if I slipped the longer bar into the next set of holes. It takes only 2 seconds to slide it into place.

The vice is really quite nice and I'm glad I bought it. I use it for 90% of the milling that I do.

Daniel

 

[gadget_lover]

Re: Work Holding - vices and such

Now that I have a collet chuck for my lathe I want to use the collets in my micro-mill too. That calls for a collet holder. If I make it with a hole all the way through I can use it in my lathe's 4 jaw chuck too for longer stock. The collet chuck has an MT3 shaft so it does not have a pass-through.

I plan to use the nut from the collet chuck to keep things simple. The dimensions for an ER32 collet are listed in the Machinery's handbook. The collet is 40 mm long, 33 mm wide with a top taper of 30 degrees and a side taper 8 degrees.

I don't have any 1 3/4 inch steel stock, but I have both square and round 6061 T6 aluminum. Can I get away with using that, or would the collets just eat it up? I'd also be concerned about the steel threads of the collet nut chewing off the threads of the holder. But then again, it might work, as it's all pretty big stuff.

I can get steel later this week, if needed. What steel would be recommended?


Daniel

 

[Iron_Man]

Re: Work Holding - vices and such

Even mild steel would be minimal for a collet holder, just forget 6061. Maybe look on ebay for what you want.

Les

 

[gadget_lover]

Re: Work Holding - vices and such

Thanks,

I'll run down to the steelyard today.

Daniel