Are Jacks Worth It?

I often find myself cutting aluminum flat bar that extends beyond the jaws of the vise. When that happens it can result in chatter or harmonics that
affect surface finish. Particularly in the actual first surfacing pass. I can go with a really small WOC, but then the surfacing of the bar starts to take up a significant amount of time.
Do you think jacks under the part are enough to reduce that or should I just start working on setting up a second vise aligned with the first on those machines?
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"Bob La Londe" wrote in message
I often find myself cutting aluminum flat bar that extends beyond the jaws of the vise. When that happens it can result in chatter or harmonics that affect surface finish. Particularly in the actual first surfacing pass. I can go with a really small WOC, but then the surfacing of the bar starts to take up a significant amount of time.
Do you think jacks under the part are enough to reduce that or should I just start working on setting up a second vise aligned with the first on those machines?
**************************
Yes I am aware that the time to make jacks is worth as much as the cost of another vise, but these are small machines with, a small envelope and a relatively small table. With one 6" screwless vise (machined to optimize envelope usage), hold downs for the vise, and an articulating work stop on the table its already quite crowded.
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I machined some cutoffs to the height of the mill vise bed and clamp the overhang of long work onto them with tee slot clamps. Thin stock can be raised to jaw top level on 1-2-3 blocks etc. I surface ground my cheaper black oxide thin parallels all to the same thickness to use as fine adjustment shims.
Low profile edge clamps: https://www.miteebite.com/products/
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On Saturday, May 26, 2018 at 11:26:36 AM UTC-4, Bob La Londe wrote:

Try hanging a good sized C clamp on the aluminum. It will reduce the chatter.
Dan
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wrote:

Add mass/restrict chatter. If not a vise, how about a 3rd hand? (No, not the type used for soldering, but larger)
A pair of vise grips on a stick might be the ticket for you. I saw one years ago but didn't save the URL. This is similar: http://weldingweb.com/showthread.php?364201-Articulated-jig
Maybe easier yet would be to weld up a piece of bar in a U shape with a vise grip on one end. Chuck it in the vise along with the bar to be cut while the vise grip holds the floppy end. I think I'll do this with one of the cheaparse Chiwanese vise grips I have which aren't good for anything else. I have that problem all the time and, like you, have never spent the time to solve it ahead of time.
--
If we can ever make red tape nutritional, we can feed the world.
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Bob La Londe wrote:

You can also put some strips of scrap on either side of the workpiece, and clamp the 3 together with C-clamps. 3 pieces with clamps are WAY stiffer than one single piece. I have some parts I make that are wider than the vise jaws, but I usually do 8 at a time. Works great with the clamps.
I have also made a custom holder for some other long parts. It is made from 3/4" aluminum, and has a step on one long corner. There are 5 tapped holes so a clamp bar can be pulled down over the step. It is a foot long. So, you put this in the vise with the edge with the step facing up, and can indicate off the step. Then, put the parts in it and clamp with the 5 screws (vertically). So, this thing is kind of a custom vise that I use for machining 3/8" square and 3/8 x 1/2" bars for a particular job.
For some other long parts, I have made up some fixture plates. One is 12 x 12", the other 12 x 24". Both have a 1" grid of 10-32 tapped holes. I made a bunch of steel clamps with 1" long slots. So, you put some bolts in strategic spots to locate the parts, and then a row of the clamps to hold it down. You can put bits of scrap aluminum under the actual part, so you don't dig into the fixture plate when machining. If you need to machine all around the part, you can move the clamps several times, as each edge is machined, always keeping a couple clamps tight so it doesn't move. The holes in the plate allow coolant to flow down to the slots and galleys in the table.
I hope all of this makes sense without pictures.
Jon
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wrote:

The jacks won't help much unless they apply pressure against the work or are somehow affixed to the work. With a typical cutter that has a helix that pulls the work up a thin part will be pulled away from the jack and you will still get chatter. If you can apply pressure to the work, say with a finger or a wooden stick, to hold the work against the jacks then the jacks will help. You can use double sided tape to hold the part to the jack, I have done this more than once and it can work very well. The jack of course must be fixed to the table for this method to work. Have you thought about vacuum? You could make up little vacuum jacks that would hold themselves to the work and the table. I seem to recall you saying you have a vacuum pump. Maybe that was someone else. Eric
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Upon Some reflection, how about a thick bar suspended between two or more jacks?
Hmmmm... I think I am getting into the area where I am just going to have to try it and see.
First I guess I need to make some jacks with different heads. Flat head, flat flanged stud head, etc.
Ultimately I am thinking I'll have to go back to the idea of shoehorning two vises on the machines. Maybe a pair of 4 inch screwless machined out to hold six inch stock to keep the weight down, and have the compact length.
4 inch mill vise or lockdown vise will not fit inside enclosure without hitting the doors. Just a hair too long. However my 6 inch screwless machined out fit just fine. I actually bought a couple 4 inch lockdowns for those machines. Oops. On the other hand they make great drill press vises. LOL.
Maybe it would be better to just sacrifice some of my tooling and make some fixtures with edge clamps.
I definitely do not need another cup of coffee this morning. LOL.
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If you don't mind modifying vises you could cut shallow work locating and clamping steps at the tops of the jaws and make support blocks the same height.
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"Jim Wilkins" wrote in message

If you don't mind modifying vises you could cut shallow work locating and clamping steps at the tops of the jaws and make support blocks the same height.
************
I definitely do not mind modifying vises. I have a bunch of screwless and except for my 1 inch insert vises which already have a stepped jaw I think I have machined at a minimum a stepped jaw in all of them. I've also machined stepped jaw or soft step jaws for most of my mill and lockdown vises. I think only the 2 4 inch lockdown vises and a 4 inch Enco swivel base mill vise I bought with some other stuff from a shop going out of business have original jaws in them. I lost count of how many vises I have a long time ago. Well over 20. Maybe over 30. I guess vises are one of my vices.
Anyway, mounting support blocks on the table and milling them to match the height of the jaw steps is a good idea. I can use 1" by X" aluminum flat bar to try it out, and then if it works upgrade to some more permanent pieces from 4140 or whatever I have on the bits and pieces shelf.
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My support block is a scrapped part from a prototype Segway.
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On Mon, 28 May 2018 12:32:08 -0400, "Jim Wilkins"

Or machine replaceable jaws in those shapes.
--
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--Robert Schaeberle
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