Milling 90 degree groove, cutter set 45 degrees in vice. How to locate Z?

[JasonBModerator @jasonb]

Would it be ok to have a couple more examples please? How can you tell the proportions will always be 1/4 and 3/4 on the 30 degree?

Tan of 30deg = 0.5774. Tan of 60deg = 1.732 so that is a ratio of 1:3 give or take a bit of rounding on the decimals.

1) What if the distance was say 20.45 on the touch off points

The distance does not matter a syou are just taking 1/4 of it so for 20.45 actual which might measure 26.45 if using a 6mm dia tool you just multiply 20.45 by 1/4 or 0.25 and get 5.1125

2) Just for another exercise to help me understand the calculations, how would this work with a angle set at 28.44 degrees?

Again you would use the same two triangle method but this time it would be

Tan 28.44deg = .5416 and tan of the complementary angle 61.56 (90-28.44) = 1.8464

Add .5416 + 1.8464 = 2.388

There for the shorter based triangle will be 0.5416/2.388 x distance call that “base 1”

and the height will be “base 1” x 1.8464

 

So if we now draw that out to check our maths again using that 20.44 measurement and the known angle of 28.44. All other sizes in brackets are what the CAD has calculated.

base 1 is shown as 4.638 compare that to (0.5416/2.388) x 20.45 and  we also get 4.638mm

For the height we now take that 4.638mm base 1 and multiply by 1.8464 and get 8.5636 and compare with 8.564mm

So allowing for my hand calculations being rounde dand the CAD showing to 3 decimal places I would say the CAD and hand calcs agree

I’ll leave it to the pedants in the membership to calculate what the allowances should be due to the different thicknesses the fag paper will measure horizontally when against the 30deg face compared to the 60 deg face😉

 

 

 

[blowlampParticipant @blowlamp]

It’s pretty straightforward if you draw it in CAD and get it to do the hard work.

As the apex point will again be missing in your 28.44 degree example, you will have to start with a fairly random Z depth when taking the two ‘touch off’ measurements from the job. This will more than likely result in an untidy distance, which in my example I’ve shown in red and is the first line you should draw in your CAD program. From there put in the 28.44 degree line as well as the one perpendicular to it which terminates at the right hand side of the red line. As before, the dimension in green is how far the tool will need to be raised to be at the apex point, whilst the dimension in black represents how far the corner of the tool was from the apex point when ‘touching off’.

 

Martin.

 

[Wade BeattyParticipant @wadebeatty78296]

Great thread and replies. Fine use of CAD and trig, most times I can just use trig, other times it is nice for the confirmation of a dimensioned CAD drawing.

 

Wade

[He Who Dares WinsParticipant @jameswilkinson3]

Thank you all for your help, it’s been very useful and I can now put these solutions to work. I want to share another solution from (Stefan Gotteswinter) on youtube.

I have made two of these now. The best one I have made is from 20mm silver steel. Cut the flats exactly at the quadrants so each one is cut exactly 10mm in. The middle hole accounts for any burrs. You can make one bigger in diameter but ensure you cut the flats at 90 degrees from each other and at the quadrants. That way, you can easily edge find the center and touch on the top, index down half the diameter to get the theoretical start point. It’s been a great tool for me.

Another great thing about these if you cut them exactly at the quadrants (half the diameter) is that they work on all angles.

There is a but though. It has to be very precisely made so you will need to check dimensions with gauge blocks and a DTI on a surface plate. The big but about this approach which is why I have been asking for another solution here is that this tool relies on the parts surfaces being perfectly square. I found it a bit fiddly to use in practice as well.

These are a great little project and a nice tool for the toolbox. Great for jobs that don’t need a very high degree of accuracy. The solutions given to me in this thread have solved my solution of finding the theoretical point precisely to accommodate for my high tolerance of 0.02mm. I just can’t trust these little “datum bars” I will call them to give me this level of precision.

Here is a picture of them taken from (Stefan Gotteswinter) youtube video. I made mine by facing and drilling the center hole in the lathe, then cutting the flats with the material set in a stevensons collet block. 🙂

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