Sunday, 25 January 2015

More Shed antics

More of a catchup post this one following on from the last post where I started this clamp setup.(Note you can click the images to view them a bit larger) I've done a bit more and made a couple more bits for it and it can now function as a dti stand for both my finger an plunger type dti's. It's still a work in progress though as I plan to make a few more pieces for it.. I quite fancy making a pair of jewellers vice to go with it and a couple of other bits. The big block it's using as a base is a bit rough and ready mainly as it is a aluminium block I opencast and then cleaned up a bit on the lathe and mill. Its cleaned up enough to have a flat base and top and 2 parallel sides meaning it can be held in a vice etc. The smaller base threads onto the larger base with an m6 thread which is compatible to all my clamping and tee nuts etc on the milling machine.

I also did another quick project out of the harold hall book today, I made a pair of parallels. Up until now whenever I've needed parallels I've always just used a couple of pieces cut from the same bar stock but I have some projects coming up which will require a bit more accuracy.

To buy parallels is quite expensive but, if bought, parallels tend to be precision ground from hardened steel so they are tougher and have astonishing tolerances. The Harold Hall book though suggests that parallels out of softer material (in this case en1a mild steel) are just as useful if treated with a bit more care. The process below is a method to reduce inaccuracies in the tramming of my case with a fixed column on my mill, it's not too bad. The first phase is you turn 2 similar(ish) diameters and centre hole them and bolts them roughly level on an angleplate set up on the mill. When turning these pieces you turn a thinner diameter on one end of each piece to be placed against the angle plate which means you can do the next stage without milling into the angleplate.

You then machine across the 2 diameters attached to the angle plate just enough that you have a flat section across the face of them. This face should be exactly at 90 degrees to the cutting face.

So the above picture shows the next phase, you clamp the 2 pieces you are going to make the parallels from to the angle plate making sure they are pressed firmly onto the flats you created. You then mill across the pair in one pass then you reclamp the pieces to mill the other side surfaces.. tis means that the first milled faces will be placed onto the flats and then the subsequent cuts should be parallel to the first side. I need to take them somewhere with a decent height gauge but Harold Hall reckons you can get them to within 0.02mm using this method. Which will do for me. Final note.. I stamped these 2 pieces as a pair 1A and 1B (mainly so I don't mistake them for just a bit of metal!) but I guess it's a good idea incase make another pair that are similar sized (but not the same). I also stamped the pieces before milling them as stamping into them might make some small deformations in size if you do it after.

1 comment:

Andy from Workshopshed said...

That milling of the supports is a good technique for increasing accuracy. Careful cleaning and a storage box should ensure they stay in good condition.