Magnetic Chucks?

[Arnak]

Hi Folks,

I am considering purchasing a magnetic chuck to use on my warco major mill.

There seem to be a variety available in rectangular and round, both course and fine.

Has anyone any experience of these chucks and can give advice on what to purchase?

For instance what is the difference between a course and a fine?

I would plan to spend around £150.

Would a second hand one be a good idea?

Thanks,

Arnak

[Staffordshirechina]

Arnak,
Magnetic chucks are normally used on grinding machines rather than mills. In the main, the cutting forces on a mill are too great and tend to move the workpiece. You can use one and take very fine cuts just to finish something awkward but even then it needs care.

Les

[Arnak]

Hi,

Thanks for that advice, I thought that may be the case.8-((

The round type seem to be listed for mills though?

Arnak

[Staffordshirechina]

Hi,
Not sure why that would be. Maybe they couldn't think of anywhere else for them? Round ones are usually for cylindrical grinding machines and would be of very little use on a mill unless on an indexer or dividing head. Even then I can't think why you would do that anyway.

Sometimes people who draw up the websites or catalogues don't really know what the stuff is - they are just told to list it!

Les

[kneedeepinswarf]

Circular magnetic chucks can also used on lathes. I have an Eclipse 5" circular chuck which is stamped "magnetic lathe chuck" by the makers, and they should know! Myford also list (or used to) a 4" Eclipse chuck for use with the ML7 and Super Seven lathes. The price of this, over twenty years ago, was about £250!
The "fine" and "coarse" probably refers to the spacing of the magnetic poles. To get maximum grip, as much magnetic flux as possible must pass through the work, from the north poles to the south poles. With standard spacing, the work has to be of sufficient thickness to achieve this, so for very thin work, fine spacing is often used.
If magnetic chucks can be used for turning, than presumably they could be used for milling, but for light finishing cuts only.
With magnetic chucks, the grip depends of the size and type of material being held. Steel gives a stonger hold than cast iron, and, within limits, larger work holds better than smaller.

[Arnak]

Hi Guys,

Thanks for your thoughts on this subject.

As I was planing to use the chuck for heavier cuts I'll give it a miss at this time and wait until I need one for the surface grinder that I intend to build asap.

Arnak

[derwent]

I have seen milling on a magnetic chuck milling cast iron, a good roughing cut, very impressive.

[Staffordshirechina]

Arnak,
I wouldn't bother making a surface grinder, they are so cheap on Ebay that you can have a proper J & S 540 for £200 - £300 if you bide your time and stalk one.

Les

[kneedeepinswarf]

Jan 28, 2009 18:26:26 GMT derwent said:

I have seen milling on a magnetic chuck milling cast iron, a good roughing cut, very impressive.

Modern chucks are impressive. Eclipse lists an electromagnetic milling chuck that gives a holding force of 150 tonnes per square metre, but I think the cost would be outside Arnak's quoted budget!

[44767]

Just by chance I bought a magnetic chuck yesterday specifically to machine the back off awkward pieces. A day earlier I had destroyed several hour's work trying to hold it with clamps to machine the back. The clamps let the piece twist and the cutter bent the piece at right angles.

I am fully aware that only light cuts can be taken and as the workpiece gets thinner, the holding power deminishes. The clamping ability can be increased by holding a piece of material a bit thinner than the finished size beside the work piece and maybe one in front. The bigger the area, the bigger the holding force. These extra pieces will act as a fence so the job can't move.

I bought a fine pole chuck (Chinese, 250 x 150mm) new for NZ$480.00 (about 177 sterling).

Do you want to see the damage to the part? I'll post a pic if you want a laugh!