Setting up on parallels

[wawoodman]

When I set up a workpiece on parallels, and then tighten the vise, the parallels are loose enough to slide out. I can sometimes beat this by getting the jaws snug, but not tight, and tapping the work with a nylon faced hammer, and then finishing the clamping.

Is this normal? Is it a sign of out-of-parallel jaws? It's an old 3" vise that fits nicely on my Rockwell mill. Do the parallels need to remain tight under the workpiece, or am I too concerned about a non-issue?

 

[george wilson]

This even happens on my new condition Kurt vise. I use a plastic dead blow loaded with lead shot hammer to seat things.

 

[kd4gij]

Yes it is normal You should always snug then tap the work down all vises wil have some lift even the kurt vise have some altho not as much as cheaper vises.

 

[Tom Griffin]

Mike,

It's normal for parts to lift when clamped in a vise. Hammering them down is a learned technique and takes a bit of practice to get it right. If you are just starting out, it helps to put a piece of paper under each corner of the work so you can tell when the part is sitting solidly on the parallels. For rough sawn parts, I like to use the ball end of a ball pein hammer. It's easy to control and if you hold the part as you tap, you can feel when it sits down on the parallels. If your part is finished, a soft hammer such as a dead blow is required. Generally, light taps work better than heavy hits, which will tend to bounce the part back off the parallels. Also, once you tap the part down tight, don't tighten the vise any more because that may lift the part again.

Here's a link to a video of mine on squaring up stock. There are lots of examples in it showing how to clamp a part in the vise.

How to Square up Stock on the Milling Machine

Tom

 

[8ntsane]

Tapping the part down is a normal thing. I a dead blow hammer that I use to tap the part down. The paralles shouldnt be loose or slide out, if they are loose, chances are the material was hit to hard and bounced back up. I like to have the hammer in one hand, and the vise handle in the other, and tighten as I tap the material down.

Tom has a good method as well. The aluminum welding rod is a good idea for rough cut parts. The ball peen hammer is good too. Ive found it as good as the dead blow, and being smaller, its easy to control. So bigger parts get the dead blow, smaller stuff the ball peen. The ball peen doesnt get used on a finished surface though.

 

[sic semper tyrannis]

And don't smack your cast iron parts too hard.

Brittle!

Oops!

 

[brucer]

check the adjustment on the front jaw on your vise, the looser it is the more chance of it pushing the workpiece up and out of square,which lifts it off the parallels..

My old machine shop teacher in high school would smack you on the back of the head if he seen you beating on a vise handle..

 

[GK1918]

I also aggree with Tom 4 pieces of paper with give "crush" and prevent any bounce.

 

[george wilson]

Who suggested beating on the vise handle???

Another way to prevent lifting is to place a piece of steel rod horizontally against the moving jaw of the vise,and pinch it between the work and the jaw. The rod will roll up,leaving the work down. Maybe this has already been mentioned.

 

[Tom Griffin]

I don't want to throw any bricks and any one method as basically the video link is a good way to square up a block assuming it's cut so that the aluminum welding wire will support the cut, if that saw cut was 1/8 off square the part will most likely lift on milling. Using 2,3,4 or more paper will do the same. On a part that small I would put something like a ball in the center. I would use 2 parallels or one with larger width so that the part not have be held while trying to clamp it. After getting one side flat I would most definitely us 2 parallels especially if the were wider. Also I feel the implication that something should be cut so that only one roughing cut is necessary is an over statement. Naturally we would all want to cut stock to size to avoid waste. However if I had a piece of 1 1/2 plate I'm not going to attempt to cut it smaller if I need 1". I would much rather cut 1/2" off on a mill than on a saw. I'm not sure where that block rough sawed aluminum came from but to saw that to size before milling seems like a lot of extra work. In my shop I have a lot of odds and ends, I'll select the nearest size saw if necessary but if I find 1 1/2 X 1 1/2 X 1 3/4 it will be milled not saw cut If I need a 1" cube.
Using digital calipers to measure .0005 is really stretching the capability of calipers. I wouldn't trust my Starrett to .005. I use a Micrometer for anything less that +/- .01 if possible. Removing and measuring and replacing the block, taking a roughing cut then a finishing cut is a gamble! I measure the part in the vise, measure after my roughing cuts and finish to size with out removing the part. After removing the part I remove the parallel , brush the vise clean, wipe the parallel and replace it. I can see the parallel rocking in the video.

Frank

Well Frank, you say that you don't want to throw any bricks, but then you throw them anyway.

I guess when I provided that link for the OP to help him visualize the technique I use for mounting work in a vise, I never thought that I would need to defend those techniques. But if you insist on throwing bricks, let's see if I can't deflect a few of them.

1) An aluminum wire works very well to fill the gaps between a rough sawn piece of stock and the vise jaw because it is soft and conforms to an irregular surface. I guess it probably wouldn't work very well if the part was sawed an eighth inch out of square, but my sister could probably do better than that with a hack saw so I think it's pretty much a non issue.

2) Using one or two parallels is a judgement call. Two are definitely the order of the day for larger parts, but for something as small as the block in the video, one works just fine.

3) I am a product of industry (over 40 years now) where time is money, and using one roughing cut and one finishing cut is definitely not an overstatement. I've worked for a lot of shops where milling a 1/2" or 3/4" off a part would get you fired in a heartbeat, in fact, I've seen it happen. Again, it's very easy to saw a part close to the finished size and it almost always saves time and money over extra time in the milling machine, not to mention the unnecessary wear on expensive tooling.

4) If you can't measure any closer than .005 with your calipers, then it may be time for a new pair. I would trust mine to a couple of thousandths even with a hangover. The comment in the video about it being a half thousandth off was apparently one of my mis-guided attempts at humor and I do apologize for that.

5) I have no clue what you mean by a rocking parallel.

I'm sure you realize that there are many different ways to accomplish the same thing in machining and whether they are right or wrong is pretty much meaningless as long as you end up making a good part in a reasonable amount of time and in a safe manner. These are techniques that I have developed over the years and they serve me quite well. If you have other methods, you should invest the time and energy into recording them for posterity (although it's not as easy as it seems). It's always interesting to see how the other guy does it.

Tom