PDA

View Full Version : Magnetic Parallels?



gzig5
10-15-2008, 04:03 PM
When and why, would one use a Magnetic Parallel on a surface grinder? I guess I can understand the use of a V-type to hold a rod, but why a rectagular one?

aboard_epsilon
10-15-2008, 04:51 PM
Maybe you're misunderstanding .
Far as I know they ain't magnetic ...that's if they look stripey in appearance with different metals laid side by side

They are of a composite construction ...and concentrate the magnetic force from the magnetic table and channel it to your workpiece

You would use them to support and get level, irregular shaped parts ...

or channel the mag force into a smaller part that could be whipped off the table.

Not used them myself ...but above are answers I've been given, when I asked about them.

all the best.markj

Mcgyver
10-15-2008, 04:55 PM
a couple of uses I've put them to....

1) when you need something absolutely dead on, take a skim cut on the parallel, eliminates any error or burr on the chuck affecting parallelism....

2) can be used a support for thin items held on edge......

3) the poles are much finer than the base chuck so for small thin work you get a better grip......

the V block parallel is also useful for.....you guessed it, grinding in V blocks

Your Old Dog
10-15-2008, 04:56 PM
You are talking about Parallels and not a magnetic chuck right? If they were thick enough, they would allow you to magnetically clamp a surface that is slightly bowed while you surface grind the other side. The grinding operation doesn't put a tremendous amount of lateral pressure on the work.

juergenwt
10-15-2008, 05:22 PM
Magnetic Parallels - used everyday by Tool and Die Makers or in Tool and Die repair work, building and repairing Fixtures and Gages.
Rectangular composite (brass or aluminum plates alternating with mild steel plates) blocks that are riveted or welded (brazed) together and than ground in pairs to a very close tolerance. Parallel and square to within +/-0.0001.
You need more than one set, each having different dim's.
Also need one or two different V-Blocks(90 deg.) and one 60-30 deg.
These are used to elevate a workpiece from a grinding chuck to provide clearance for sections of a workpiece protruding on one side and you are trying to grind the opposite side. Many other uses to numerous to mention.
Also available are magnetic V-Blocks that swivel in a base and can be set at different angles.

gzig5
10-15-2008, 06:25 PM
Ok, seems to be about what I thought...fixturing odd shapes. Hadn't thought about the thin stock on edge, that was a good one Mcgyver. I've got a Rockwell surface grinder I am rebuilding and have seen the magnetic parallels for sale but never in use. They might be handy for some of the things I have in mind for this machine.

I take it that there is not much loss of holding force compared to using the chuck surface directly? I'll be using a 5x10 B&S magnet that seems to hold pretty well. Maybe not as strong as the electric vises I've used, but should be sufficient.
Greg

Teenage_Machinist
10-15-2008, 09:01 PM
It may not be as strong but small stuff will be much safer. I am guessing that they are good for things like mill tables that cannot just sit flat.

Peter S
10-15-2008, 09:02 PM
I take it that there is not much loss of holding force compared to using the chuck surface directly?

Greg,

Using the terminology from an Eclipse catalogue I have to hand - there are chuck blocks (the laminated type, made in pairs e.g. Eclipse No. 950) which simply transfer the magnetic flux of the chuck into the workpiece - they are common in surface grinding work when you have an underside projection, I think we used to call them transfer blocks. It is years since I have done any grinding, but I am sure there is a loss of power. Maybe use extra blocks at each end of the workpiece to help anchor things and take great care.

Then there are also magnetic parallels, these being precision-made pairs, but with their own magnets which can be turned on and off, (Eclipse No.929).

Then there are the magnetic vee blocks (Eclipse No. 934), but as well as these toolmakers use their own (non-magnetic) square blocks of all shapes and sizes to hold parts both square and round using toolmakers clamps etc.

Apologies for repeating some info already given, really just pointing out that I think there will be a loss of power using the chuck blocks.

lazlo
10-15-2008, 09:07 PM
There are chuck blocks (the laminated type, made in pairs e.g. Eclipse No. 950) which simply transfer the magnetic flux of the chuck into the workpiece

I am sure there is a loss of power. Maybe use extra blocks at each end of the workpiece to help anchor things and take great care.

The non-magnetic magnetic parallels :) definitely lose power from the original surface, especially if the width of the bronze/aluminum lamination strips don't match the width of the poles on the chuck.

As you've probably noticed, there are fine-line magnetic chucks, which are better for holding thin, flat stock, and there are thick-pole magnetic chucks which are better for holding bulky items.

gzig5
10-17-2008, 11:48 AM
Thanks All. I think I've got it.

Timleech
10-17-2008, 01:20 PM
As you've probably noticed, there are fine-line magnetic chucks, which are better for holding thin, flat stock, and there are thick-pole magnetic chucks which are better for holding bulky items.


There are also adapters which fit onto a coarse-pole chuck and convert it into a fine-pole, as here:-

http://home.btconnect.com/duttondock/images/Mech/Handraulic-2a.jpg

Tim