Magnetic parallels for surface grinder

Matt Matt · Nov 15, 2018

I’m wondering if anybody else has made a set of these before? And how efficient are they?

About 25 years ago I made a set, but I never got to use them. The grinding hand got me to make them when I was a apprentice. The grinding hand used them about once a month, that I saw.

I have a 30 pole magnet on my surface grinder.

I was thinking of making them from 4140 annealed and leaving them soft. About 2 1/4” tall.

I do have an 18 inch magnet with 23 inches of stroke. I figure the longer they are, the more powerful they will be.

I do have a custom job that needs custom height. Initially I am thinking of making them 10 inches long and maybe in the future making some 24 inches long.

Alex McGilton · Nov 15, 2018

I have a set made by Fisher machine shop, and yes they do discernibly weaken the magnetic field when a piece is placed above. one reason that certainly contributes is that the plates are not equivalently spaced, so like a vernier some of the lines line up and some don't. For the set you intend to make you may as well make the plates equally thick so they can be aligned perfectly to maximize the field strength.

I would be cautious about use of 4140, it has a high carbon content and chromium like austenitic stainless steel it may make for a weaker transfer of a magnetic field. Here is a chart of magnetic permeability. Mild steel may be a better choice, if anything it is cheaper.
2�181115_231326.jpg - Google Drive

Permeability

Matt Matt · Nov 15, 2018

Thanks Alex. My thought on 4140 was I have a little bit of sitting around the shop. My thought was on mild steel (which I have a lot of it sitting around the shop, is just possible damage. I have a lot of offcuts from die punch holders that I build. I do realize the chromium content in 4140 is a little bit problematic. But I’m trying to find the best of both worlds).

When I made the set as an apprentice I had to skip poles. I’m making a drawing up as I’m typing this. My surface magnet poles are .300” and my insulator between each pole is .200”.

So, the poles for my Parallels will be .300 with a airgap of .700 . I’m figuring this will take my 30 pole magnet and turn it into two poles at the top of the parallels. This would be a skip pole parallel. I’m still wondering about the strength?

I haven’t seen this repeated any shop since for the last 25 years. This is why am wondering about the quality of magnetism. I can’t remember what I made the parallels from, for the grinding hand 25 years ago.

Your link shows magnetic transfer blocks purchased. I have aboat a dozen sets of these in V and Square.

Wlodek · Nov 15, 2018

I think that the steel for any magnetic application should be almost pure iron. I would go with A1011 or similar.

Matt Matt · Nov 15, 2018

Wlodek said:
I think that the steel for any magnetic application should be almost pure iron. I would go with A1011 or similar.

For my test Parallels, I’m thinking about using just simple mild steel, I’m thinking using 1/2-3/4 thick CRS and stealing the old man’s design . The old guy was highly talented(about 65years old, was not a dummy). He is now probably on the other side of the fence looking down. This is probably the only project he was happy about, that I did for him. Otherwise I was ducking from flying blocks when I screwed up.

I learn the hard way...

gbent · Nov 16, 2018

Your blocks should mirror your chuck for steel width and spacing. They should be placed so the parallels align with the chuck.

Matt Matt · Nov 17, 2018

gbent said:
Your blocks should mirror your chuck for steel width and spacing. They should be placed so the parallels align with the chuck.

The old man they got me to make these once before are a dedicated designing, only two poles of the entire magnets. These are’t normal parallels or mag blocks with aluminum or bronze brass insulators. They use alternate poles. The parallels need to be shifted to pick up the alternate poles.

dian · Nov 17, 2018

Toolmakers magnets - Part 1 - YouTube

i believe stefan made parallels as well, but i dont see them now.

MushCreek · Nov 17, 2018

I made a magnetic V-block using a chunk of brass, drilling in a lot of holes in a staggered pattern, and pressing in steel (I used nails!). It works well on most magnets, but gets dicey on very small parts. I've also used 1-2-3 block sized parallels made the same way. I've mostly used commercially made cast parallels, but it's expensive stuff. I've always wondered what kind of steel they used.

Matt Matt · Nov 17, 2018

Magnetic parallels that I’m talking about are not the same as magnetic blocks. They do not have or contain any magnets in them. They do not have any aluminum or brass in them. They actually run perpendicular to the poles on the magnet.

adama · Nov 17, 2018

Poles in the chucks face are just mild steel wny do you need a ocasionally used thing to be any harder? Its going to have reduced magnetic properties, its also going to still be more than soft enough to get scratched by the odd grain of lose grit off the wheel when dressing.

Nice thing with good old CRS and normal bright mild steel, they won't take - hold much of a magnetism, hence your part will still release when you turn off your chuck.

I second make the pole spacing match the chuck for best results.

Illinoyance · Nov 17, 2018

gbent said:
Your blocks should mirror your chuck for steel width and spacing. They should be placed so the parallels align with the chuck.

So I have a micro pitch chuck. Should I assume my Fisher parallels aren't going to work?

gbent · Nov 17, 2018

Illinoyance said:
So I have a micro pitch chuck. Should I assume my Fisher parallels aren't going to work?

They will still work, its just a question of how well. No matter the difference in spacing, at some frequency the poles will still align perfectly, and the wrongly spaced poles will still transmit some magnetism. As always, check the hold of your part before starting. Blocking may be advisable.

Matt Matt · Nov 17, 2018

Well I did find an old punch holder backing plate. I do assume it to be 4140 or maybe mild steel. It is 0.610 thick. It is just shy of 8 inches long.

All cut

Here’s my drawing

Matt Matt · Nov 18, 2018

I roughed on the pole steps. Took it to the magnet a and I am about 60% impressed. Hopefully I get time tomorrow and I’ll grind them up. While milling, I kind of came to the conclusion that mat is 4140. I only milled the pole keyways 0.525 deep. I’ll grind them up nice and then maybe add in the radius.

sable · Nov 18, 2018

How about drill and tap the ends so you could add a little end stop.

dian · Nov 18, 2018

Matt Matt said:
Magnetic parallels that I’m talking about are not the same as magnetic blocks. They do not have or contain any magnets in them. They do not have any aluminum or brass in them. They actually run perpendicular to the poles on the magnet.

im confused. all my "magnetic parallels" have brass (or whatever) in them. i mean if you put a piece of iron on the chuck, it wont work, right?

Matt Matt · Nov 18, 2018

dian said:
im confused. all my "magnetic parallels" have brass (or whatever) in them. i mean if you put a piece of iron on the chuck, it wont work, right?

Yes and No.

If you see how I milled them and see how they are sitting on the magnet one picks up all the north poles and transfers it up as a single north pole. The other one picks up all the south poles and transfers it up as only one south pole. It shifts the magnetic field. It works very similar to a lifting magnet that only has two poles.

So the eight little legs are picking up eight North poles in one parallel and the other parallel is picking up with it’s eight little legs, eight South poles.

CarbideBob · Nov 18, 2018

dian said:
im confused. all my "magnetic parallels" have brass (or whatever) in them. i mean if you put a piece of iron on the chuck, it wont work, right?

The OP has replaced the brass with air.
Yes not exactly but for all intents and purposes an nice hack that I've not seen.
Air gap (depth) in the slots must count and of course it has to be sat on the chuck correctly.
Bob

sable · Nov 18, 2018

So this only works with a pair of parallels .

Magnetic parallels for surface grinder

Cast Iron

Cast Iron

Cast Iron

Aluminum

Cast Iron

Diamond

Cast Iron

Titanium

Aluminum

Cast Iron

Diamond

Stainless

Diamond

Cast Iron

Cast Iron

Titanium

Titanium

Cast Iron

Diamond

Titanium

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