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Project Halo
Stilldrillin:
John,
That was so very well done, and very well shown..... :clap:
The sort of thing many thousands of skilled machinists have done many times, over very many years.
But, very difficult to explain to others....... ::)
You have the knack. :headbang:
David D
spuddevans:
--- Quote from: Stilldrillin on August 05, 2009, 02:20:14 AM ---John,
That was so very well done, and very well shown..... :clap:
The sort of thing many thousands of skilled machinists have done many times, over very many years.
But, very difficult to explain to others....... ::)
You have the knack. :headbang:
David D
--- End quote ---
I agree totally with David D. Thanks for taking the time to show those of us who are not trained machinests just how to save a lot of time and effort to achieve a consistent result using a jig. :thumbup: :thumbup:
Tim
kvom:
I am very impressed with the jig, esp. with the thinking that went into it. Seems simple once you understand it, but I would not have come up with anything close. Using the oriented flats to ensure the 45 degree angle between top and bottom was the part I found ingenious.
I would be using round bar, but would have milled the flange square first, thus reducing the fabrication to the square bar case.
bogstandard:
Many thanks for the comments.
Unfortunately, having thought about it, I was a little selfish just showing how I had done it, and ignoring how most other people would do it with the square bar.
So I hope this post will correct that.
What I did this morning, was to do a setup as if I was doing it by the square bar method, but not actually drilling any holes. So you will have to use your imagination a little.
Just imagine this isn't another drilling jig, but the square bar with the bore thru it.
This is what I would do.
Put the backstop in position, with a pair of parallels in the vice. The low tension spring is to keep the paras in position as you are opening and closing the vice jaws all the time, and it is a PITA if you have to keep resetting them. Then I put my favourite edge finder in the chuck. You will have to allow for slightly different operations if you use another type.
You should, if possible when doing drilling like this, always work from known fixed points. The two fixed points here are the vice fixed jaw and the back stop.
So the part is dropped onto the paras and pushed against the stop and jaw with a downwards pressure as well, then the vice is tightened up.
I shouldn't need to remind you that the ends that go down onto the paras should be faced off and square to the sides.
This is a part I must explain to you. If you have machined the square bar yourself, it should be to size. If it came as a purchased length, sometimes the size can be up to about 0.005" smaller. This must be taken into account if you want good accuracy, and as such, you should measure the bar both ways, and make allowances.
We will take an example of the bar being 0.004" smaller. Halve the deficit, 0.002", and subtract that from the amount you have to move inwards from the edge. The further from the fixed faces the measurement is, the more critical you remove the error.
If you are working from the centre of the part to a PCD measurement, the centre of the bar must be found by subtracting the errors first.
I have done a rough sketch at the end to show what can happen if you don't do it.
A lot of times it doesn't make a difference, but if you are working to tight tolerances, it does.
So you find the edge, and move over the correct amount.
Then do the same thing on the backstop side.
So you now lock up X and Y axis, then using a centre drill, put in your pilot hole.
Move the part around to the next side and drill in again. The green spot represents where the first drilling was done, I told you it was imagination time.
So once all four holes have been pilot drilled, put your twist drill in the chuck, set up for correct depth, and drill away. You repeat for all four corners.
During the turning process, you have to make sure that all the areas are kept clean, because a bit of swarf can easily knock things out of line.
So for the other end, you repeat the first setup but using a different sized drill and locations.
As above.
As above, but if the size difference isn't allowed for, these holes, being out of line, will have more impact on the job.
This is a very rough sketch of what will happen to the holes if you don't compensate for the difference in size.
This pic is in fact wrong, I have shown the bar offset centre position in the wrong place.
Just use your imagination again, and think of it as being right.
I hope you had enough imagination to pick the technique up.
Bogs
CrewCab:
Good tips John, many thanks :beer:
CC
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