Sets of parallels

[Mike PooleParticipant @mikepoole82104]

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

[Chris MateParticipant @chrismate31303]

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

[DiogenesIIParticipant @diogenesii]

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..

[JasonBModerator @jasonb]

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

[Bill PhinnParticipant @billphinn90025]

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.

[John HaineParticipant @johnhaine32865]

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).

[Old SchoolParticipant @oldschool]

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

[Anthony KnightsParticipant @anthonyknights16741]

I find HSS tool blanks make pretty good parallels.

[RobCoxParticipant @robcox]

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.

[John HaineParticipant @johnhaine32865]

Oops.

[Tony Pratt 1Participant @tonypratt1]

Posted by RobCox on 16/12/2021 08:36:47:

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.

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

[GordonHParticipant @gordonh]

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.

[VicParticipant @vic]

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.

[Nicholas FarrParticipant @nicholasfarr14254]

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.

[Tony Pratt 1Participant @tonypratt1]

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

[not done it yetParticipant @notdoneityet]

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…

[RobCoxParticipant @robcox]

On a surface grinder you might well have trued up the top of the mag chuck with the grinder itself (I did) so it's top surface mill will be co-planar with the plane of travel of the table.

You could achieve the same on the mill I guess, skimming the base of the vice where the workpiece beds to make it co-planar to the table travel, but I doubt many of us would want to "modify" (being polite) our milling vice like that.

[DiogenesIIParticipant @diogenesii]

Posted by Bill Phinn on 15/12/2021 20:04:14:

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.

..I think Harold deliberately wanted to illustrate a method capable of producing the most accurate result, with the most basic of equipment.. ..the same book gives details on how to convert a cheap drill-press vise for use on the mill, it was somewhat before the advent of the small, but decent and cheap, milling vices we enjoy today.

There're pictures of the finger-type clamps he favoured here – using one of these in the middle slot should hold a pair of parallels okay, be sure to set it so that it doesn't cause the parallels to 'kick-out' when tightened;

Harold Hall – Angle Plate…

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