Making magnetic transfer blocks

MichaelP · Oct 13, 2012

I wonder if anybody wants to share experience on making magnetic transfer v-blocks and parallels. In particular, I'm interested in those with ferrous metal pins (vs. laminated), so that they can be placed on the chuck at any angle.

Is it just a simple drill, ream and press fit type of deal? What's the best steel to use for the pins (magnetic quality wise yet easy to handle)? How to choose the most efficient diameter and number/concentration of the pins to increase the hold? Would you prefer bronse, brass or aluminum for the body and why?

Any thoughts, tips and technics (including those on best manual machining approaches to cut accurate Vs) would be appreciated.

Thank you.

Mike

ADFToolmaker · Oct 13, 2012

I'm not an expert, but have made them successfully in the past. What I made were rectangular blocks, laminated from mild steel and aluminium strips, not for any reason, thats the material we had. The laminations were held together with aluminium rods, riveted over into a countersink on the first and last laminations, which were steel. I did not spend too much time accurately machining the holes for the pins, they were a loose fit. Once the assembled block is ground the pins are just to hold it all together. All the same I was surprised how firm the stack was just from peining over the aluminium pins into the countersink.

cash · Oct 13, 2012

For the ones with pins you will want to use a brass body and then mild steel pins. We make these often. This configuration for us transfers the magnetism the best. You get knurled pins and then just press them in. Depending how big you want to go I have the pins in stock.

But for a Vee block I don't see what you can't make them like they normally are with a mild body and then brass laminations. I believe these are brazed together just like magnetic chuck top plates.

Milling the Vee is the easy part. Grinding it so that you are dead center on size is the tricky part. We have tried to tune up an old set but just could not get them good enough. When we had a new set made I had to send back to be touched up.

Our blocks are about 18" long, 4 " wide and maybe 1.5" thick.

PixMan · Oct 13, 2012

How big are the blocks you want to make? If it's the common small sizes, just buy them unless you're a retired home shop guy with way too much time on your hands.

I bought these as one lot on eBay for $40, shipped. No way I could begine to make them for that kind of coin.

If you need large ones such as what cash needs, now you're doing the right thing by making them.

cash · Oct 13, 2012

PixMan said:
How big are the blocks you want to make? If it's the common small sizes, just buy them unless you're a retired home shop guy with way too much time on your hands.

I bought these as one lot on eBay for $40, shipped. No way I could begine to make them for that kind of coin.

If you need large ones such as what cash needs, now you're doing the right thing by making them.

I believe this style with the stainless are pinned and then welded on the end.

MichaelP · Oct 13, 2012

Guys,

Let me underline again, I'm interested in making pin type blocks, not the laminated ones (although I enjoyed reading ADFT's description, anyway). Nothing really large: they will work on my 6x12 grinder.

Cash, so you just use 1018 for the pins? As far as I understand , the steel of choice should have a high magnetic transfer, but low residual flux qualities.

What size of pins do you have and used? Any rules in terms of choosing the diameters and distance between the pins? Any reason you chose brass vs. aluminum for the body?

And accurate preparation of the V is indeed, what I'd like to hear tips and thoughts on.

TDegenhart · Oct 13, 2012

Magnetic Pin Blocks

Is this what you mean by pin block?

I don't know how these were made, they came with the gerstner tool box 50 years ago from a toolmaker that went off the bench. They appear to be nails cast in epoxy.

Tom

MichaelP · Oct 13, 2012

Yes Tom. These are the type I'm talking about. The modern ones are made of brass or aluminum instead of epoxy, and the pins are, usually, larger and spread more apart. I suspect that yours may hold parts stronger, however.

They differ from the laminated type by the fact that they can be positioned at any angle relative to chuck poles and yet transfer the flux very well.

Here is one of my parallels

ADFToolmaker · Oct 13, 2012

cash said:
For the ones with pins you will want to use a brass body and then mild steel pins. We make these often. This configuration for us transfers the magnetism the best. You get knurled pins and then just press them in. Depending how big you want to go I have the pins in stock.

But for a Vee block I don't see what you can't make them like they normally are with a mild body and then brass laminations. I believe these are brazed together just like magnetic chuck top plates.

Milling the Vee is the easy part. Grinding it so that you are dead center on size is the tricky part. We have tried to tune up an old set but just could not get them good enough. When we had a new set made I had to send back to be touched up.

Our blocks are about 18" long, 4 " wide and maybe 1.5" thick.

Cool I'm going to make some of these for sure, much easier than laminations.

CMT John · Oct 13, 2012

When we made these during my apprenticeship an amazing old school toolmaker had us use nails in a brass body. It was seen as a great grinding exercise. There is more to grinding a V block than many people realize.

MichaelP · Oct 13, 2012

John,

Stop teasing. Elaborate please.

TDegenhart · Oct 13, 2012

MichaelP said:
What size of pins do you have and used? Any rules in terms of choosing the diameters and distance between the pins?

As a rule, the shorter the pin and the larger in diameter, the more efficient is the flux transfer. The problem is that the large pin diameter works best with a very coarse magnetic chuck. The large diameter effectively shorts out the poles on a fine pitch chuck

The field equations are not hard to write or solve but in general one can use the relationship,

magnetic efficacy ~ D/4L^2

Where D - diameter of the pin, L - length of pin

But as stated above, the large cross sectional area does not do a good job of capturing the flux from the chuck.

The greater the spacing of the pins, the less leakage flux, therefore the more effective the pin bock.

i.e., when you are done designing the rocket, you still have to make one to see if it will fly.

Tom

MichaelP · Oct 13, 2012

Tom,

Thank you for the very interesting info. So I guess I should choose pin diameter that will be just smaller than the distance between the chuck poles (I have fine poles, by the way) and position them apart from each other yet so that my parts cross a few pins resting on the block.

TDegenhart · Oct 13, 2012

Since they are very simple to make, I would suggest making one each and judging which works best.

Tom

Forrest Addy · Oct 13, 2012

Never made them but the process should be simple enough if a bit tedious. I always wonder at the thickness of factory block laminations and why they never suited the pole pitch of any mag chuck ever made in the universe.

I think I'd use steel lams thick as the iron of the chuck poles and brass lams wide as the space between. Line up the iron to the poles and you should get max magnetic transfer.
'
Of course they may not suit a different chuck but is that a problem if every grinder has a custom made set?

The process? Make stacks of lams a bit oversized on the edges and sil-braze them together holding alignments close as possible. Then machine/grind to size and geometry.

winger · Oct 13, 2012

I'm not sure why but with the sets I've used, the brass laminated blocks seem to transfer better than the aluminum laminated. I haven't used pin type blocks though.
Dave

lowCountryCamo · Oct 14, 2012

A stupid question... why are they laminated instead of solid? I googled that question before asking here but found nothing.

Billtodd · Oct 14, 2012

why are they laminated instead of solid?

Because the magnetic flux has room to turn back on itself in a solid block or if the gap between laminations is too small.

I think you'd be better off with Iron pins (soft iron nails would seem an obvious choice) Steel will magnetise and hold on to any magnetic dust etc.

Casting in a block of resin is a great idea , the resin only has to be strong enough to keep the pins from toppling over .

dgfoster · Oct 14, 2012

TDegenhart said:
Is this what
you mean by pin block?

I don't know how these were made, they
came with the gerstner tool box 50 years ago from a toolmaker that
went off the bench. They appear to be nails cast in
epoxy.

Tom

Billtodd said:
Because the
magnetic flux has room to turn back on itself in a solid block or if
the gap between laminations is too small.

I think you'd be
better off with Iron pins (soft iron nails would seem an obvious
choice) Steel will magnetise and hold on to any magnetic dust
etc.

Casting in a block of resin is a great idea , the resin
only has to be strong enough to keep the pins from toppling over
.

At first when I looked at Tom's shop-made resin-cast
pin blocks I marveled at the regular close spacing of the pins and
wondered how the guy that made them ever held them so neatly. Then
two thoughts came to mind:

1) Find a perforated metal screen with the appropriate size and spacing of holes. The variety made is
amazing so it should be possible to find what you would want. Then
cut a couple of rectangles of the screen and make a picture frame of
anything convenient. I think I would just use wood. Then attach the
screen on the front and back of the frame so that the holes line up.
Drop in nails to fill the holes. Pour in resin. Once it is set up the
rest is obvious.....

2) Alternatively, find thin sleeving material. Could be plastic or metal. slip sleeves on the pins
covering a portion of the tops and bottoms of the pins. Stack the
sleeved pins together in a box. Pour in resin and away you
go.

Either of those methods would be a lot quicker than
drilling closely spaced holes in brass. The brass would likely be
more durable in heavy use though.

Idle musings.....

Denis

CMT John · Oct 14, 2012

As Cash said,the grinding of the V block is the tricky part. You want to start out getting your block absolutely square. A couple of tenths this way or that out of square will make it impossible to get the V square and pointed the right direction.

Before you even get started this is a very good excuse to regrind the chuck on your surface grinder. I like to use a Magnetic sine chuck, now is the time to touch that up making sure it's nice and flat and no wear, dings or burrs on the side rails.

Yes, this is all pretty basic stuff, but skipping any of the basic steps will have you chasing you tail all day trying to figure out where the error is coming from.

.

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