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Preventing the marring of aluminum in vise jaws, parallels

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chris.trotter

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#1
So I've run into a new issue - while I am flycutting/squaring up my aluminum stock, I'm marring the faces with the vise jaws and parallels. I had stoned the vise jaws previously. The parallels when I'm smacking it flat, the vise jaws are hit/miss as to whether or not they mar.

What's the correct way to deal with this?

apr19-surface_marring.png
 

derf

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#2
Pad the faces with card stock, like a business card or the like.
 

Mitch Alsup

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#3
What is the application that requires non-mared starting stock?
 

chris.trotter

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#4
Well....that is a curious question. You imply it's normal to have marred starting stock...? These are pieces i'm flycutting to square, to give me a clear starting point on my project.

I could re-face once done, but I'd have similar issues, no?
 

Mitch Alsup

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#5
You missed the point::

Most of the time, square stock get machined to final shapes and sizes, and those mars will disappear when the metal is re-cut.
While this is happening, you are continuing to use parallels, and knock the stock onto the parallels. So whatever you are doing to cause those mars, will continue to be present all the way through the end of the machining. So mars will always be present.
 

chris.trotter

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#6
I think we're saying the same thing. So how do you prevent marring in general is maybe the better question?
 

agfrvf

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#7
Jaw pads softer than what you cutting. Copper, brass, lead...
 

mikey

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#8
Chris, the issue you're having is probably due to tapping down to get the work solidly down on the parallels and the tops of the jaws are digging into the work. The work is not yet square so naturally the jaws dig in. This is a technique issue.

Try this.
  • Find a round rod, ideally aluminum, and put it between the work and the moving jaw of the vise. Try to place the flattest face of the work against the fixed jaw, insert the rod so it lies parallel with the bed of the vise and tighten the vise. The rod holds the flattest face against the fixed vise of the jaw but allows it to tilt a bit if that face is off square, which it is. Fly cut the top.
  • Turn the work so the flycut surface is against the fixed jaw and the bottom of the piece resting on the bottom of the vise or a single parallel sitting against the fixed jaw; this first flycut surface is now your reference surface. Re-insert the rod and lock it down, then flycut the second face; this second face is now 90 degrees to the reference surface.
  • Flip the piece 180 degrees with the reference face still against the fixed jaw; insert the round rod and lightly close the jaw, then tap the second face you cut into firm contact with the vise bed or single parallel and flycut the third face. Now you have three faces all 90 degrees to each other.
  • Remove the rod, put the reference face on the bottom of the vise or on two parallels if it is thin, then lock the piece in the vise. You now have three square sides and when you clamp down, nothing digs in. Flycut the top and you now have four square sides.
  • You can now either switch to an end mill and square the ends or stand the work vertically in the vise with the reference face against the fixed jaw; use a square to ensure the sides are vertical and fly cut the first end. Once that is square, flip it 180 degrees, put the fly cut end on the bottom of the vise and fly cut the last end.
You should now have a square work piece with no marring.

No mystery here. Just proper technique for squaring a rough work piece. Some of us use a ball bearing with a flat ground on one side that goes against the movable jaw instead of a rod; it works but the rod is easier to grab and use if the work piece is not too out of square. The ball works better for really rough stock where nothing is close to square. One more thing: after fly cutting each face, deburr the edges before re-clamping it in the vise.
 

P. Waller

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#9
Wire EDM, in this method of machining the tool never contacts the work so it requires little or no clamping force, this will solve your problems yet has drawbacks of its own as you might imagine.
 

chris.trotter

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#10
@mikey that is exactly the process I was doing (although your explanation has been the clearest I've seen on this subject so far), the marring is happening when I'm hammering the piece into place on the vise. When I have two parallels under the reference surface, the front parallel is loose until I really mash on the workpiece with a deadblow hammer (made extra difficult because my mill is tiny). Further, when you say 'lightly tighten the vise and tap with hammer', this doesn't work. When I fully tighten the vise the front side lifts - my vise is really a glorified drill press unit. I suspect the only way to get past that is to get me a decent vise.

The card stock trick might help, though, given that I have to mash it - worth a shot.

Also lol at wire edm. When I was in college, we did a tour of a plant doing wire edm, super cool stuff. Massively outside the capabilities of my humble home shop, however. :D If there's gonna be another large machine, it'll be a surface grinder.
 

mikey

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#11
Chris, sounds like its time to buy a decent vise. Trying to get a work piece to register solidly on parallels when the dynamic jaw can move or rise is going to frustrate you. Have you considered a screwless vise? Even the Chinese ones are pretty decent.
 

chris.trotter

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mikey

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#14
Chris, I don't know which mill you have, if you enjoy this machining stuff enough to stay with it or what your budget is so I'm basing my comments on a guess; please keep this in mind.

A milling vise is the heart of the mill. It holds the vast majority of the work you will do, and the accuracy of the vise is directly reflected in the accuracy of your parts so a cheap milling vise is rarely a good choice. The problem with good milling vises is cost. A Kurt or Glacern vise is not cheap to buy or ship, especially to Canada, so a lot of hobby guys buy import vises and make do. That's okay; not a judgement. However, I wouldn't do it.

Personally, I would buy a decent import screwless vise that has published specs while I save up for a really good milling vise. Screwless vises are actually more rigid and potentially more accurate than milling vises, although they are a bit slower to use. If I could only have one vise, it would be a screwless vise.

I own two milling machines, a Sherline and an RF-31 benchtop mill. I have a US-made Wilton precision milling vise and a US-made Wilton precision screwless vise for the Sherline, and I have a Kurt D40 vise for the RF-31 and a 4" import screwless vise, too. l use the milling vises on both machines most of the time but when I need the best accuracy, I switch to the screwless vises on both machines. I don't recall the brand of my 4" screwless vise but I recall the published specs say it is accurate to within 0.0002" on all faces; when I checked it, it was accurate to within 0.0001". It just beats my Kurt in this regard so I use it when I have an important project.

My point is that you don't need to spend a ton of money on a milling vise right now. Buy a decent screwless vise and learn to use it. They are actually quite good. Later, when funds become available or a good deal drops in your lap, buy a good milling vise. Better this than spend money on a cheap vise that won't give you the accuracy you need.
 

JCByrd24

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#16
The Shars line of vices are great for the price and I will be going there if the $90 one that I bought with my PM ever leaves me wanting more, so far it’s been fine. It has a pull down feature that’s rougher than the Kurt and way better than any drill press vice could hope to be.
 

chris.trotter

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#17
@mikey Thanks for the input. I think for the time being I'll be ok with what I have. I tried out the cardstock trick @derf mentioned - using some old business cards - worked a treat! The reality of my situation is that accuracy is less of an issue than lacking tooling, I'd rather buy a boring head, collets, rotary table, etc, than a vise that'll give me repeatability and accuracy. I'm such a noob right now, that's a next step kinda thing. :D

I do have a screwless vise, too - just no clamps for it (see other thread where I butcher that project). It's just a little one - 2" - so I tend to only use this vise.
 

mikey

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#18
Okay, but just so you know, if the vise is off then everything you hold in it is off. The vise is the heart of the mill and I consider it essential. On the other hand, you gotta go with what you feel is right.
 

chris.trotter

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#19
Yeah, totally get and appreciate that. From what I've been doing so far I am able to make a pretty darn square block (doing the light test using a machinist square), so am confident in that regard. I'm not making parts for money or anything, or for anything requiring (any) degree of precision (right now). Eventually I will get a nice vise, just not while I'm satisfied with the current quality and still lack basic tooling.
 
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