More lathe gadgets

[Mayhem]

(03-01-2015, 08:24 PM)stevec Wrote: Could the magnets influence the operation of the DIs?

Steve

I actually added a magnet to the back of a DI and it did mess with the operation.  The magnet was strong enough to influence the workings and with the magnet on it wouldn't zero consistently.  I replaced the metal back plate with one I made of copper and it works fine now.

[Micktoon]

Hi All, just an update on the mag DTI's after working fine with the metal 'shield' between the magnet and the DTI the other day both just held in my hand or stuck to the lathe bed, the magnet appears to have 'soaked ' into the DTI and its now not returning 100% when held in my hand and sticking badly when atteched to the lathe. They are both the same too.
  So a plan B is needed, I too had thought Copper or brass or even lead but looked on google and it seemed to say a shielding metal had to be magnetic itself ?
  I think the whole topic of magnets will get bigger and more complicated the more you look, all I want is my DTI'S to stick to the bloody lathe without jamming not to become an expert on magnetic fields so does anyone  know the correct way to overcome the problem ? 
  Cheers Mick

[Mayhem]

Double-sided tape

[awemawson]

My plunger / diesinker EDM machine uses magnetically attached DTIi's by original design, which dates from probably the 1980's. Never had any problem with the DTI's action. However the magnets, which are cylindrical, are recessed into a steel block and surrounded by a brass tube, so forming a sort of toroidal horse shoe magnet. By this design I presume that the lines of force are directed away from the DTI

[f350ca]

I've had a magnet stuck to the back of the one on the left for years, that's why I was joking with Steve.

Its been on there so long I don't remember how I attached it or where the magnet came from, but the magnet is set in a metal shell.

[Vinny]

Many eons ago I worked for an alarm company. When a magnetic switch was installed on a steel doorway, the magnet on the door had to have a plastic spacer (or two) between the door and the magnet or the magnet wouldn't reliably close the switch. The door would eventually be drawing the magnet's pull. The spacers were about 3/32" thick.

Now, that said and with Mick's discovery I think I'll make a plastic block to cover the mount on the back of the ones I just got and sink a magnet in that. I'll report back (with pics) after I do it.

[Micktoon]

Hi Vinny , thanks for your reply, the DTI's I used did have flat plastic backs on them as standard, I am not sure how thick as I have not taken one off but the plastic seemed to have no effect at stopping the magnetic field because with out my added steel sheet the magnet just stopped the plunger returning at all  
  Hope you have better luck but I would try with just holding things together before spending too much time making anything properly jsut to prove the concept................ saying that , thats what I did and the bugger worked until I tried it again

  Cheers Mick.

[Vinny]

The plastic's cheap (I buy 2 gallons of resin at a time) and I need one anyway.

[Vinny]

Here it is.  I still need to find a magnet around here.  I have plenty of hard drive magnets but they're still in the hard drives.   I also need to add a bit more plastic to the bottom, it's a bit thin in the middle as you can see. It measures 1.125" x 0.750" and the little hole in the side has a 6-32 set screw in it holding on to the DI.  I did it that way 'cuze I have a DTI that's smaller in diameter and the tab on the back is smaller than these.

Thinking about it now, what I should've done was just made a plastic cylinder and milled the hole for the DI tab afterward.

Seeing how it came out, I'm going to make a mold of it so I can make more.  

[Micktoon]

Hi  Vinny , I have some PVC bar I think I will turn some and make a similar type plastic stand off as yours and give that a try, thanks Mick