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Black Forest
09-22-2011, 05:54 AM
I want to build a two part vice very similar to the one in the picture.

My question is, how important is it for the screw that pushes the movable vice jaw to be a acme thread?

The three blocks of the vice will be 45mm x 45mm x 150mm.

Second question, I like the idea of a shelf in the faces of the jaws to sit something on to bore through or drill. How deep in both directions do you all think would be good? I work mostly with steel.
http://i853.photobucket.com/albums/ab91/burnandreturn/two_part_vice.jpg

Tel
09-22-2011, 06:52 AM
Well, in my 'umble opinion the Vee form thread would be fine. As for the steps? Probably around 0.1" each way

Your Old Dog
09-22-2011, 08:14 AM
I think the V thread would work for occasional use but the Acme is obviously a much stronger thread as it has more support for long term use. Unless you don't have time to wait for an order, I'd take the time to do it with Acme. I found it very reasonable price wise. I bought some rod and nuts just to have around incase Stevenson were to ever darken my door.

J Tiers
09-22-2011, 08:26 AM
The V thread will work JUST FINE.

In fact it will probably WORK BETTER than any Acme thread, simply because it is going to be finer, and can get more force on the work with less "work" on your part. (Yah, acme has a tad less friction... whoopee).

I'd say go for it.

Consider using TWO screws. Can hold better in some situations.

Here's mine

http://img.photobucket.com/albums/0803/jstanley/vise1.jpg

JCHannum
09-22-2011, 09:42 AM
The thread is not a big deal, one screw or two would depend on the width of the moveable jaw. The outer guide rails are a good idea.

I would suggest that the screw be installed at an angle, pushing down on the moveable jaw to overcome the tendency of the jaw to lift under pressure.

Black Forest
09-22-2011, 09:48 AM
I can certainly see why you used two screws as you only have on t-slot. I would just be concerned with uneven clamping. Though I am not sure exactly why I am concerned!

I have thee t-slots 90mm on center. My plan is to use two guiding rods 27mm in diameter and a 20mm thread to clamp. If for some reason I don't get enough clamping I could easily add two more one on each side.

J Tiers
09-22-2011, 11:09 PM
I would suggest that the screw be installed at an angle, pushing down on the moveable jaw to overcome the tendency of the jaw to lift under pressure.

Depends where and how the screw presses on the jaw..... in the back, it isn't so effective.

I use the hold-down screw to pull it down again and seat it.... that and/or a lead hammer.

The two screws work better than you may expect..... if you have perfectly square workpieces, no issue, but if they are out of square, guide rods jam up, but two screws give you a way to compensate and hold tight, if not too outrageously unsquare.

Paul Alciatore
09-22-2011, 11:45 PM
I also would consider two screws. If you are worried about their capacity to hold, use a high grade screw and more than the usual number of female threads. Also a larger diameter screw would have greater holding power.

darryl
09-23-2011, 12:41 AM
You have the choice as well of going with a finer thread. More holding power for less torque, less chance of it loosening through vibration, but slower adjusting at the same time. I don't think the choice of thread type will make any difference- keeping them lubed with a light oil or something will make a difference.

As far as the depth of the step- I'd go 7/16, and I'd go 3/16 the other way. You can use 1/4 inch square key stock as a spacer, and also 1/8 key stock. That way you can handle 1/2 inch thick stock without the spacers, 3/8 stock with the 1/8 spacer, 1/4 inch stock with just the 1/4 inch spacer, and 1/8 thick stock with both spacers. The ledge being 3/16 wide lets the 1/4 inch spacer sit on it without falling off, and any other spacer would sit well also.

I'll make another suggestion- when you have the movable jaw 'finger tight' so it will still move as you tighten the vise, the movable jaw will lift off as you tighten it. You can go through a couple of steps to optimize the process, but the end result that you want is for the movable jaw to stay against the table. To get that you'll need the hold-down bolts fairly tight, which means that the nuts under the t-slots will want to stay in place while the jaw moves. The hold-down bolts will tend to lean, which in turn will pull the jaw downwards, but will also rob the adjustment bolt of some of the pressure it's exerting. Ideally you'd want all the pressure from the adjustment bolt exerting to close the jaws.

To help this problem, you could arrange for the nuts to be pushed along simultaneously with the jaw. On my mill, the t-slots are 1 inch wide underneath, so I made several nuts from 1 inch x 3/8 thick bar as part of my clamping kit. If you made nuts the same way, there's no reason why you couldn't drop a pin down from the movable jaw, which would go through a hole in one end of the nut. As the jaw is moved along, the pins move the nuts along as well. The bolts stay upright and will clamp more securely.

Another thing- the wider the jaws are, the better they will stay flat on the table, and if you make at least the movable jaw wider, there will be lots of room for the pins. You could use 1/4 inch music wire for the pins. You can also pin the other nuts, and the benefit is that they are kept from rotating as you feed the jaws onto the table. Once in the slots they won't rotate, but it would be nice if they could be kept lined up while the vise parts are being fitted onto the table. The other pins don't need to be any more than 1/8 in diameter. All of the nuts need to be able to slide easily on the pins, obviously.

Speaking of pins, you could also put some holes vertically in the fixed and movable jaws. You could insert pins, which gives you another option to hold parts which may be odd-shaped.

boslab
09-23-2011, 01:00 AM
I rekon vee would be ok but i would be wary of off the shelf bolts as the effective only needs to be a it low and the bugger may strip on you, flying workpeices are very unfunny and could hurt you and your machine! we dont want that!
Traditionally square thread, butress [best] or acme were the ones with the biggest contact area to dissipate the load of heavy clamping, you could buy a bar length of one of them or canibalise an ebay vice! [record vices over here are handy as they sell spare bolts and nuts, kurt probably do too]
regards
mark

Black Forest
09-25-2011, 02:56 PM
I decided to make the vice as wide as my table. 250mm

The blocks are 48mm square. The rods are 25mm chromed hydraulic rod for a hydraulic cylinder.

The rods slide perfect. I will have three holes in each block to attach the vice to the table. There will be two screws to apply pressure.

The hard part is done. Tomorrow I will finish the vice I hope.
http://i853.photobucket.com/albums/ab91/burnandreturn/vice2.jpg

Black Forest
10-03-2011, 02:32 PM
I finished my vice. It is 230mm wide. In the pictue it is I made everything except I welded a spark plug socket on the screw so I could use a ratchet to tighten the vice. I mill a 3mm x 3mm shelf on the face of the jaws. I am thinking about milling a vee in the jaws to hold round material. both vertical and horizontal.

There is no brass in this vice!!!


http://i853.photobucket.com/albums/ab91/burnandreturn/finishedvice.jpg

Tony
10-03-2011, 02:38 PM
Nice job!

Though the 4th, 5th, and 6th thread turns look like brass to me!

ok ok .... maybe its bronze. ;)

keep us posted as to how it works out for you.

aboard_epsilon
10-03-2011, 02:41 PM
Too late now ..but you can get good acme threaded rods out of scissor jacks for projects like this.

all the best.markj

Black Forest
10-03-2011, 02:46 PM
I actually used it to make some T-nuts to use with the vice. The shelf held just fine when I milled the T-nuts. I purposely located the screw a few mm higher than on center with the slide rods. My thought was it would help to push the movable jaw down. I think it works as planned. With the vice turned the other way on the table and bolts in all six holes I put my 3d Taster on the top of the movable jaw and clamped a piece of steel. I indicated the top of the jaw and then tightened the T-nuts for the movable jaw. The indicater needle did not move.

lazlo
10-03-2011, 03:08 PM
Very nice! I have to "borrow" that design :)

Black Forest
10-03-2011, 03:39 PM
Danke Lazlo. I take that as a condimetn!