Author Topic: Picking up and milling a internal tangent line to two radii  (Read 976 times)

Offline 90LX_Notch

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Picking up and milling a internal tangent line to two radii
« on: September 07, 2018, 01:59:59 AM »
In my current build of George's four cylinder, I needed to mill a tangent to two different lenth radii in an internal pocket (Red line in first picture).  Initially, I was going to sweep them with an indicator; but quickly realized that, one it would be a pain in the bottom; and two, it most likely would be prone to error.  What I came up with was the following:

1) Place two ball bearings against the radii.
2) Place a tool bit against the bearings.
3) Set an indicator against the tool bit.
4) Squeeze the tool bit and move a bearing back and forth watching the indicator.
5) The bearing is set when the indicator indicates it's lowest point of travel.
6) Repeat 4 & 5 for the second bearing.
7) Indicate the tool bit as if indicating a vise jaw and adjust the part until the indicator reads zero.

Once the tool bit indicated zero, I proofed the method by removing the bearings and starting over.  The tool bit indicated zero without any further adjusment of the part.

-Bob
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Offline Kim

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Re: Picking up and milling a internal tangent line to two radii
« Reply #1 on: September 07, 2018, 04:48:37 AM »
Bob,
Thanks for sharing this! It is quite clever - or very simple - or both, which makes it even better!
I saw that on your other thread and wasn't quite sure what you were doing, but this explanation made it very clear to me.  Thank you for taking the extra time to write it in simple language for newbies like me!
Kim

Offline 10KPete

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Re: Picking up and milling a internal tangent line to two radii
« Reply #2 on: September 07, 2018, 08:04:50 AM »
As we learn those tricks, the better we are able to learn more.

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline Lew Hartswick

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Re: Picking up and milling a internal tangent line to two radii
« Reply #3 on: September 07, 2018, 01:24:23 PM »
That get the right angle just fine BUT the start and stop points are where I'd probably goof . :-)
   ...lew...

Offline 90LX_Notch

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Re: Picking up and milling a internal tangent line to two radii
« Reply #4 on: September 08, 2018, 12:59:23 AM »

 Kim- Thanks. I'm happy that it was clear.


Lew-

Regarding the starting and stopping points, I set my stops for X short of the centers of the radii by eye.  Since the part was zeroed on the rotary table for the center point of the bigger radius, the tangent point for Y was the radius minus 1/2 the cutter diameter.  The cutter was then set to the depth of the pocket and I side milled the wall until I was within .010 in Y.  Then I unlocked the stops and increased the travel in X and watched by eye.  At this point, once a pass was completed, I increased Y in .001 increments until I was happy with it.

I hope this makes sense.

-Bob
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My Engine Videos on YouTube-
http://www.youtube.com/user/Notch90usa/videos

Offline Lew Hartswick

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Re: Picking up and milling a internal tangent line to two radii
« Reply #5 on: September 08, 2018, 02:01:56 PM »




Lew-

Regarding the starting and stopping points, I set my stops for X short of the centers of the radii by eye.  Since the part was zeroed on the rotary table for the center point of the bigger radius, the tangent point for Y was the radius minus 1/2 the cutter diameter.  The cutter was then set to the depth of the pocket and I side milled the wall until I was within .010 in Y.  Then I unlocked the stops and increased the travel in X and watched by eye.  At this point, once a pass was completed, I increased Y in .001 increments until I was happy with it.

I hope this makes sense.

-Bob
Ah Yes. If the center of one of the arcs "still there" That will be a BIG help. :-)
   ...lew...