Convex Radius Program

[Chewy]

I have seen this answered before, but now that I need it I can't find it. I need a program to calculate stair steps for cutting a large convex on a mill. The stock is 3/8" X 1-1/2" X 5" 6061. It is a butt plate adapter for a Savage 99. My boys eyes aren't all that great and he wants to try out my father in-law's gun. The stock is too short for him, so we are thinking about adding a recoil pad. I want to make an adapter to fit the gun so as to fit a flat recoil pad without cutting the stock. It's an older gun in excellent condition and I want to put it back in OEM condition.

I played around with the math stuff and came up with a 9.4098 R over 4". Ran it though CAD and cut out a 100% piece and it is pretty darn close. The only way I can do this is to do a set of measurements in CAD every 15-20 thousands and use the DRO. Will the DRO directly calculate all the steps for me? Can somebody send a link to a calculator that will do all this for me? I want get close enough to hand file to fit the gun stock.

Thanks in advance!!!! Charles

 

[RJSakowski]

I have seen this answered before, but now that I need it I can't find it. I need a program to calculate stair steps for cutting a large convex on a mill. The stock is 3/8" X 1-1/2" X 5" 6061. It is a butt plate adapter for a Savage 99. My boys eyes aren't all that great and he wants to try out my father in-law's gun. The stock is too short for him, so we are thinking about adding a recoil pad. I want to make an adapter to fit the gun so as to fit a flat recoil pad without cutting the stock. It's an older gun in excellent condition and I want to put it back in OEM condition.

I played around with the math stuff and came up with a 9.4098 R over 4". Ran it though CAD and cut out a 100% piece and it is pretty darn close. The only way I can do this is to do a set of measurements in CAD every 15-20 thousands and use the DRO. Will the DRO directly calculate all the steps for me? Can somebody send a link to a calculator that will do all this for me? I want get close enough to hand file to fit the gun stock.

Thanks in advance!!!! Charles

Check your DRO for an arc routine. My Grizzly has one and you can set it up easily. It will only cut in a single quadrant so for ard angles greater than 90º, you have to run two or more. You can set it up as coarse or fine as you wish. Too coarse and you have stair steps, too fine nad it borders on insanity. The program basically gives you the distance to move x and y to reach the next point. You move until the DRO reads 0,0.

It is possible to accomplish this if your DRO doesn't have this function but it is even more tedious. A spreadsheet will help with the calculations and reducing errors.

 

[Flyinfool]

I had to do a similar thing on one of my rifles. I made the extender out of wood, Drew the arc using the stock as a guide, cut the arc on the metal cutting band saw, and then lay sandpaper into the concave arc of the stock and slide the new part back and forth to sand it to a perfect fit. It has held up fine for the last 30 years.

 

[Chewy]

RJ found what you are talking about in the DRO manual. Trying to decipher the setup. Going to take a piece of scrap and see what happens. I was thinking about someone posting a spreadsheet set of numbers.
Fyinfool, hadn't thought about wood the way you did it but I will try that over the next couple of days. I have the paper template for layout and a 14" brand new Jet band-saw to cut it out. Should have some poplar scraps about.
Gonna be a learning experience!!!

 

[RJSakowski]

To use a spreadsheet, I would place my DRO 0,0 coordinates at the center of the arc. Pick an angle increment small enough to suit your needs. As an example, say I wanted to cut a 4" radius arc starting at 12 o'clock and ending at 3 o'clock. On my mill the start point would be 0º and 0.0000,-4.0000. The end point would be 4.0000, 0.0000. 120 equal steps will give me about .050" steps. This amounts to .75º/step.

In the spreadsheet I would set up a table with the angles from 0º to 360º in .75º increments in column A (this allows me to use any start/end angle combination). In Excel, the angles have to be entered as radians so I would create a second column (B) to convert the angle to radians. In the next column (C), I would enter the equation =R*sin(B) and in the fourth column, =R*cos(B). Then I would copy these two for all of the angles. This generates my table of coordinates.

Note that R should be equal to the radius of the cut less the radius of the tool for an inside cut and the radius of the cut plus the radius of the tool for and outside cut.

I have set up a spreadsheet if anyone is masochistic enough to want to do this.

 

[Flyinfool]

I have done the spreadsheet thing when I had to cut a double intersecting cam profile. It took a long time to cut in 1/2° increments. The cam profile had to be cut 12 inches long in a chunk of 1045 steel, it took a couple of days.

 

[Chewy]

RJ, sure glad you understand what you just told me. I will try to plug that into the DRO. Math is not my strong suite. I do have a secret weapon though. My daughter is a math wiz. I will forward your directions to her with my requirements. She was going for her Math Masters when she quit teaching. She now grooms dogs for actually more money and tutors at night. The difference being that her students want to learn and not just occupy space. If I did what she has told me about school, my parents would have whipped my A-- or told the teacher to.

If I understand you. I will start at 0,-.215 and end at 2,0. than rotate the piece and redue. The arc center height is .215 and 1/2 the chord is 2"

Looks like the wood plug will be first. I have to learn how to do this on the mill because I have a couple of jobs for my wife's boss that will need this skill. My boy just dropped this on me and I'm trying to catch up. He of course has researched all this and knows how simple it is.

 

[RJSakowski]

RJ, sure glad you understand what you just told me. I will try to plug that into the DRO. Math is not my strong suite. I do have a secret weapon though. My daughter is a math wiz. I will forward your directions to her with my requirements. She was going for her Math Masters when she quit teaching. She now grooms dogs for actually more money and tutors at night. The difference being that her students want to learn and not just occupy space. If I did what she has told me about school, my parents would have whipped my A-- or told the teacher to.

If I understand you. I will start at 0,-.215 and end at 2,0. than rotate the piece and redue. The arc center height is .215 and 1/2 the chord is 2"

Looks like the wood plug will be first. I have to learn how to do this on the mill because I have a couple of jobs for my wife's boss that will need this skill. My boy just dropped this on me and I'm trying to catch up. He of course has researched all this and knows how simple it is.

It sounds like you have different parameters on your DRO. On mine, I first enter the plane I am working in (I have a three axis DRO). Next, the coordinates of the center of the arc, followed by the radius of the arc, the coordinates of the start point of the arc, the coordinates of the end point. the cutter diameter, the direction of tool compensation, and finally, the maximum step. If I needed to cut outside of the quadrant, I would start a new run with the first end point as the start point and a new end point. Strange things can happen if yo try to start and end in different quadrants. Also, Defining a radius, a center point, and start and end points over-define the the parameters. As a result, you have to make sure that the start and end points agree with the center point and radius. This isn't too difficult for 90º arcs but can be for differing length arcs. If you are laying this out in CAD, you can obtain start and end coordinates from your CAD drawing.

 

[Chewy]

OK, I think I understand what you are saying. I will take what you said along with the DRO manual and give it a try. It had a whole lot more steps than your first post. Looks more like what you are saying now. I don't know all that much about the DRO. Use ABS, INC, PCD mainly. Never tried an ARC before. Most of the stuff I do I layout or CAD the item and just go to that position. From what you just said above, I will cut the whole arc at one time without flipping the part. Or do I have that wrong? I will be using XZ according to DRO manual. I will be cutting in Y and I should move the table in X steps to get the arc over the long length of part.

I plan on laying out the arc. Cut or end mill the bulk of the material out of the way. Switch to a 1/4" endmill and than run the program. I have lots of scrap metal around to try to understand the setup.
I do appreciate your help.

 

[Chewy]

Wood spacer made! Took a piece of good pine and rubber cemented the CAD drawing on top. Glued a handle on backside that also kept wood vertical. Hit a lick on disk sander and that was it. The stock has a turn down at both ends, so I glued the cut off pieces back on upside down. Biggest problem was get the holes centered with wood perfect. Had to elongate holes to get wood to settle in place. After that, I sanded the plate and recoil pad on attached gun. Didn't have a big enough, long enough screwdriver to remove stock. Got drill rod to make them, just haven't got around to it.
The pad was painted and attached to gunstock with very fine layer of black silicone adhesive. There were a couple of spots where you could just see daylight between the two pieces of wood and the silicone solved that. The recoil pad sits just proud of the stock. The top I over sanded, and I can live with that. I expect to have to redo some of this or change scopes as the focal distance doesn't look right to me now. That will be up to my son. The stock has been extended and the gun has not been altered. It can return back to original butt plate easily.

Flyinfool-Thank You!!!!

RJ I will do he ARC soon. I need to make a punch press for a very large radius piece of plastic. I made a temporary one out of aluminum and than filled in the rough arc with JB weld. It has worked for the last couple of years and now I want to make a hydraulic press version. I may PM you for help.