Sets of parallels

It's not hard to make parallels with parallel long edges that 'will do' for most work, using a method I think I absorbed from ?Harold Hall;

Cut some strips of gauge plate / ground flat stock close to finished size and 'true' one long edge of each.

A couple of discs of scrap steel are bolted to a small angle plate with washers behind to hold them off the face, and the top of the discs skimmed, bringing them parallel to the table.

Without disturbing the set-up, the 'true' edges of your proto-parallels are placed across the freshly-cut tops of the discs, firmly seated and clamped, and the upper edge trued - with a little care, the end result will be as close to parallel as your machine is able to achieve..

It's possible to find quite large lumps of GFS surprisingly cheaply, and with a bit of foresight and planning , it's a quick 'Saturday Mornng' job to knock out a few pairs of different heights..

It goes without saying that there's no point hardening them, they will warp - I view them as consumable, but a generous chamfer avoids 'high-spots' if I drop or hit them and they seem hard wearing enough as is..

It goes without saying that there's no point hardening them, they will warp

Agreed, but need not be a problem (and advantageous) if they are machined to final dimensions after hardening and tempering.

Warco are selling a set like this, see my earlier post, at about £75

Sorry for overlooking your post, Baz.

DiogenesII, (you're a cynic?), could you say how you recommend clamping pieces of ground stock to the angle plate? I'm assuming they're like yours, i.e. without holes.

I have one very large parallel that I use for clocking the mill vice if I feel I want it to be a little more accurate than just clocking the fixed jaw, the large parallel is about 12” x 1.75” x .75” . Just nipped in the vice this gives a very long clean face to clock. It does mean a lot of winding of the table so the enthusiasm is not always there to go for the maximum check.

Mike

Thanks for all the advice, thats a lot of perspective on parallels.

Bill - I just used some small G clamps, with a block to act as a 'stop' at the end(s) if desired, but engineer's clamps would be okay - because the edge is only thin, light cuts with a sharp cutter don't pull the work around too much.

I did a couple of passes 'climbing' (to push the work against the 'plate) with a new and very sharp 8mm cutter and job done..

Bill, If you have 3 slot sin your angle plate you can do it as Harold shows in his book

Thanks, Diogenes and Jason.

I haven't got a copy of Harold Hall's book unfortunately. A link or image would be appreciated if possible. My only angle plate at the mo is one of the adjustable ones with T-slots (rather than holes).

Is there a reason why HH suggests this method to cut parallels (i.e. rather than using your usual milling vice)? Is the method aimed at people who as yet don't actually own any parallels?

I've made parallels using my milling vice and, as far as my measuring can establish, they are as close a pair as the shop-bought ones I have.

The reason for using an angle plate is that there are fewer constraints on parallel thickness - in a vice you have to have a parallel thinner then the one(s) you're machining whereas on an angle plate the only constraint really is your clamp. The other point about machining your own, just to repeat what I pointed out above, is that you should machine both edges and when you turn them over to to the second side you turn them END FOR END keeping the same sides facing you. This ensures that even if the bottom of your vice isn't parallel to the table the two edges of the parallels should be parallel to each other (though not exactly at right angles to the ends).

I make a lot of thin parts, steel rules make good parallels over the years I have amassed a good collection of them.

I find HSS tool blanks make pretty good parallels.

I thought the reason for the angle block and the discs, which have flats milled on them is to ensure the flats on the discs are exactly parallel to the plane of the cut the mill takes. That way, when the blank is milled one side, flipped and milled again, the two milled sides of the parallel are exactly that, parallel.

If the base of the vice is not coplanar with the plane of the cut taken by the mill and one edge of the blank is seated against the base of the vice, whichever way you rotate it and recut it you will always cut a taper.

Oops.

The angle block & discs is a good way of removing some error inherent in vices, even if the angle plate is out of square to the m/c slides you can get parallel top & bottom faces by first machining one edge with say side A clamped to the plate & then m/c the 2nd edge with the opposite side B clamped to the plate,this is assuming A & B are parallel.

Tony

The HH method is to fit the two buttons to the angle plate, each offset slightly by a washer. The top of the buttons are then milled to provide a base location for the bottom of the part to milled. This location is parallel the plane of the milling cutter. The part is then clamped to the angle plate, located against the buttons, milled on the top face, turned top to bottom and the new top face is milled. This produces two parallel faces.

I ended up with quite a number of pieces of ground flat stock which I simply cut to length. Using two pieces from the same bar has worked for me. I just left them soft.

Hi, excuse my crude sketch and I have exaggerated the angle a bit, but the two buttons on the angle plate will work out fine, however, it also needs the side of the angle plate to be in the same plain as the cutter, otherwise you could end up with a pair of "parallels" with a shape as shown on the left and right. A way to overcome this is to mount a plate on the angle plate with the buttons and machine the face of the plate true to the cutter plain. You can of course have the same situation with your vice.

Regards Nick.

Nick, when I posted my reply to Rob Cox I was aware of both conditions but the LH one is the best of the 2 but as you say you could machine the side of a sub plate and then mount against that.

Tony

If I wanted them parallel, to the nth degree, I would set them across a vise on the surface grinder and check for parallelism over a sufficient length. Then, if necessary, shim the vise (to provide the precision required) and go from there.

Somehow, I doubt that, over a short distance, the surface grinder mag chuck would be outside my requirements - but something to check sometime…