Hello Guest it is April 15, 2021, 09:04:00 PM

Author Topic: Mirror probing  (Read 1975 times)

0 Members and 1 Guest are viewing this topic.

Mirror probing
« on: March 30, 2019, 08:55:18 AM »
I have never done any probing. How user friendly is it? I need to probe and cut a mating part. Basically the matching convex to a tapered radius. Just for multiple one offs of different parts, I doubt I will ever reproduce the same part.  I am trying to decide which way to go. Probing or build a tracer attachment.
Re: Mirror probing
« Reply #1 on: March 30, 2019, 04:42:01 PM »
Hi,
I assume from your description that you are using a lathe?

You need to turn a part to mate with a convex mirror?

Probing you may be surprised is remarkably easy and you can make an adequate probe yourself without spending
anything. It occurs to me you could try it without a great deal of expense or time.

Can you explain a bit more about what you are doing?
Can the convex surface be mounted in your machine to probe it?

Craig
My wife left with my best friend...
     and I miss him!
Re: Mirror probing
« Reply #2 on: March 30, 2019, 06:08:35 PM »
Sorry a little more info. This is a hurco knee mill that I retrofitted, basically an oversized Bridgeport. This is for making rifle quarter ribs. I made a tracer for my old manual mill but I sold it with the mill. With that I made a casting out of epoxy by pressing the barrel into it, then copied the contour. I was thinking with probing I could set the barrel up and probe the area I want to fit the rib to and then mirror it somehow. So if you aren’t familiar with quarter ribs, it is basically a piece or steel mated to the top of the round barrel and soldered on. This is where the sight is then dovetailed into.
Thanks
Don
Re: Mirror probing
« Reply #3 on: March 30, 2019, 06:59:29 PM »
Hi Don,
OK that makes sense.

I see a couple of challenges that might occur if you probe the barrel.
First I imagine for a solder joint to be effective accuracy is important, say less than 0.001".
If you were to probe in the Z direction accuracy of the probe data would be good at and around the centerline
of the surface but accuracy would degrade as you approached the flanks of the surface. If that loss of
accuracy is a problem then the probe axis would have to be rotated such that it was approximately at
right angles to the surface.

That would not be insurmountable but adds considerable complexity.

How 'far around' the barrel does the quarter rib have to extend?

Craig
My wife left with my best friend...
     and I miss him!
Re: Mirror probing
« Reply #4 on: March 30, 2019, 07:08:13 PM »
I could set it up at 90 to use x y ?  Here is an example
Re: Mirror probing
« Reply #5 on: March 30, 2019, 07:31:01 PM »
Hi,
that is quite a complex shape and so I would guess that simply probing in the Z axis direction would
not be good enough.

Yes if you rotate the barrel OR alternately the probe then you would get better results. The data collected would
form a 3D point cloud. That gets away from the rather simple G31 probe command.
I'm not saying it cant be done but that extra complexity will give you cause for thought.

My strength is Mach4 and with Mach4 you can have up to four probes. What I would do is have one probe
operate normally, ie vertically and two others operating at 900 to the first ie horizontally,
one in the positive Y direction and one in the negative Y direction.

To my knowledge all three probe point data would still end up in the one probe file and would constitute the
raw data for a 3D point cloud.

How you would go about that in Mach3 is a little more problematic. I suspect it could be done but I would
defer to Mach3 gurus.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mirror probing
« Reply #6 on: March 30, 2019, 07:45:19 PM »
I wouldnt be opposed to Mach 4 if that is something that could be done in the hobby version. I would just need to work a couple things out for an upgrade. Good food for thought.
Thanks
Don
Re: Mirror probing
« Reply #7 on: March 30, 2019, 07:50:45 PM »
Hi,
yes, up to four probes is common to both Mach4Industrial and Mach4Hobby.

I might point out that I feel sure something could be cobbled together in Mach3 just as well, its just I'm not sure
how. Changing to Mach4 on this basis alone might be dubious.

Craig
My wife left with my best friend...
     and I miss him!

Offline MN300

*
  •  243 243
    • View Profile
Re: Mirror probing
« Reply #8 on: March 30, 2019, 07:54:03 PM »
I Googled "quarter rib dimensions" and see the side touching the barrel appears to be defined by 2 dimensions.
http://www.scoutrifle.org/index.php?topic=2580.0
Quote
Dimensions are as follows: A = barrel diameter under the center of the front pair of screws
                                      B = barrel diameter at the chamber
It should be a relatively easy job to make a CAD file for this.
Are the dimensions of the top details specific for different brand scopes? Are these published?
Re: Mirror probing
« Reply #9 on: March 30, 2019, 08:27:51 PM »
Problem is unless you contour the barrel yourself which is rare there is no way of knowing the barrel dimensions short of measuring it yourself. And many are hand polished so that changes everything. In the past you would make a dam to hold epoxy and make a reverse cast of the barrel then just copy with a tracer mill or tracer attachment. This is one of the instances where the dimensions are irrelevant as the part is custom fit and the next one will be different.
Thanks
Don