Author Topic: Cutting a spherical radius  (Read 2916 times)

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Offline Cat Whisperer

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Cutting a spherical radius
« on: January 30, 2005, 10:28:08 AM »
Well, I don't have THE piece of steel I want for the radius cutter yet.

So I'm using the time to rough cut the waste material by making straight cuts at a 45 degree angle.  Putting into AutoCAD it looks like most of the metal will be removed by this method.  That's good, because it's easier to crank that handle on the cross slide than work the bar of a radius cutter.


Tim K                 www.GBOCANNONS.COM
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Offline Cat Whisperer

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Cutting a spherical radius
« Reply #1 on: January 30, 2005, 12:19:21 PM »
Getting there.  45 degree bevel is 1.6" wide (need 2.1).


Tim K                 www.GBOCANNONS.COM
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Offline CU_Cannon

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Cutting a spherical radius
« Reply #2 on: January 30, 2005, 01:11:56 PM »
For my coehorn I stepped the radius off.  By using the formula for a circle as r^2=x^2+y^2 you can find the coordinate of any point on the circle.  I made a excel file to make things easy.  

http://www.geocities.com/jeanluc83/cannon/round.xls

To use the file enter the radius you want and the cut size.  

It turned out ok.  It didn't come out exactly round but that was more because I got impatient.  It took quite a bit of filing but it didn't turn out to bad.  I'll upload a pic of it to my golf ball coehorn thread.

Offline Cat Whisperer

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Cutting a spherical radius
« Reply #3 on: January 30, 2005, 02:48:36 PM »
I did consider that method, but since this is an operation that I'll be using often, it's worth it to me to make the radius cutter.  In addition to mortars I'm sure that I'll be making a few cannon balls and certainly bullet and spherical ball moulds.

I do, however, much admire the ability to do what ever it is with very little for resources!
Tim K                 www.GBOCANNONS.COM
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Offline ShadowMover

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Cutting a spherical radius
« Reply #4 on: January 30, 2005, 04:02:50 PM »
Maybe some variation of this guy's ball turning tool would work?
http://www.metalwebnews.com/howto/baltool/balltool.html
It looks easy enough to make.

Offline guardsgunner

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Cutting a spherical radius
« Reply #5 on: January 31, 2005, 08:45:15 AM »
Shadowmover,
  I have both a 2" and 4" ball cutter of simular design. Mine are steel and of a little  heavier  construction. They indeed are easy to make and really worth the effort.

Offline Cat Whisperer

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Cutting a spherical radius
« Reply #6 on: January 31, 2005, 12:49:30 PM »
Quote from: ShadowMover
Maybe some variation of this guy's ball turning tool would work?
http://www.metalwebnews.com/howto/baltool/balltool.html
It looks easy enough to make.



The choice is between that style and doing one horizontally.  I'd like to build one that will do from an inch to just over 8".  8" diameter will easily clear, but I have to offset a bit to get the lower bearing low enough (inbetween the ways) to do the 8" diameter sphere.  I've got a large selection of bearings, just have to get the right material and cut it to the right shape.  Being lazy, I'm looking for something right-much close to the right size to begin with.  As with the fellow who posted (above quote) I've passed on a number of commerically built $600 second hand cutters on Ebay.

Thanks for posting the plans!
Tim K                 www.GBOCANNONS.COM
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Offline Cat Whisperer

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Cutting a spherical radius
« Reply #7 on: February 06, 2005, 10:53:29 AM »
Well, it's almost done.
First attempt at building a radius cutter that is.

The lever and stainless shaft are from a palet of JUNK that I bought  $25 from work (included two Bridgeport 6" vises).

The arm is 1/4" x 2" CRS, and the 3/4" bolt is a hold-down bolt from a new MAZAK work center.

The 'tool holder' is a block of steel I use to hold two boring bars - 1" and 2" or so.  Serving another duty here.

Need to build the tool holder yet.


Tim K                 www.GBOCANNONS.COM
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Offline GGaskill

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Radius cutter
« Reply #8 on: February 09, 2005, 12:50:37 PM »
I think the inside arm is way too light weight for your application.  It is going to need to resist the entire cutting force reaction and I expect it will flex and give you an unacceptable amount of chatter if it develops enough force to cut.

Also by cutting on top, you will be developing a substantial moment about the lathe bed.  It would be much better to cut from the bottom to the center if there is enough room to do so.
GG
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Offline Cat Whisperer

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Cutting a spherical radius
« Reply #9 on: February 09, 2005, 02:35:18 PM »
Good analysis, I agree with you.  This is just a quick first attempt at cutting a radius.  I know full well that I'll probably only get to make light cuts.  But what it will give me is experience at a low cost (LOTS cheaper than the $600 second hand ones on ebay).  The next one will have two bearings (not just slip fit steel on steel) and be well supported on top an bottom (between the ways) and be big enough for a 8" bowling ball and will have the capability do to concave as well as convex.
Tim K                 www.GBOCANNONS.COM
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Offline Cat Whisperer

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Re: Radius cutter
« Reply #10 on: February 12, 2005, 07:40:37 AM »
Quote from: GGaskill
I think the inside arm is way too light weight for your application.  It is going to need to resist the entire cutting force reaction and I expect it will flex and give you an unacceptable amount of chatter if it develops enough force to cut. ....


Took the 1/4x2 piece and added two 1/4 x 1 pieces to form I-beam shape.  Helped a lot.  Still have a chatter coming from looseness in main bearing area - the 1" hole is just drilled and not reamed so it's a little loose.  But with light cuts it's working.  I'll definitely do heavy duty bearings (TWO of them) on the next edition.  Good exercise in learning.
Tim K                 www.GBOCANNONS.COM
Cat Whisperer
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Offline Max Caliber

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Cutting a spherical radius
« Reply #11 on: February 12, 2005, 07:55:33 AM »
Sir Cat:

How about some more pictures before you finish the lathe work.

Max
Max

Offline GGaskill

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Cutting a spherical radius
« Reply #12 on: February 12, 2005, 10:08:00 AM »
It might help to weld a block in place (drilled for the pivot) where the arm mounts on the pivot.  The thin stock there seems like a source of flex.
GG
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Offline Cat Whisperer

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Cutting a spherical radius
« Reply #13 on: February 12, 2005, 11:38:14 AM »
OK - here you'll see the reinforced inner arm before cutting the radius.  Acutally very little has to be removed because of the three linear cuts at 45 degrees and that + and - 22-1/2 degrees (in above drawing).

Then the cutting done, polishing with abrasive, welding the trunions and some cleanup with wire brush.  

After this my wife and I went out for dinner, came back, and the steel is still hot - as we speak.



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Tim K                 www.GBOCANNONS.COM
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Offline GGaskill

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Hemisphere
« Reply #14 on: February 12, 2005, 04:43:53 PM »
That came out pretty good.
GG
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Offline Cat Whisperer

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Cutting a spherical radius
« Reply #15 on: February 13, 2005, 03:07:59 AM »
Thanks GG.  The next one will be easier and will look lots better.

I've got a bit of time invested - learning, and about $10 in steel.

I've learned that a 4 independant jaw chuck holds much more securely than a 3 jaw scroll chuck.

I've learned that I need sideways as well as vertical support when cutting the pockets for the trunions.

I've learned that the diameter of the trunion should be the same size or smaller on the outside.

I've learned where I need greater strength in the radius cutter.

I've learned that a pointey cutter doesn't chatter much where a curved one will, allbeit the smooth one will give a smoother cut when held securely.

I've learned how critical the bearing slop is in the radius cutter in preventing/causing chatter.

I know I can weld better, I just need to put that mind-set in place when welding and take the time.

So thanks to y'all for your advice and interest.  It has been a good exercise.  Base is next.  Wood for this one.
Tim K                 www.GBOCANNONS.COM
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Offline Powder keg

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Cutting a spherical radius
« Reply #16 on: February 13, 2005, 04:37:23 AM »
Super Job! I've been a machinist for 12 years and I still learn new stuff every day. Isn't it Great! I really like that barrel. Great! Another project. I've built several cannons/mortars with welded on trunnions and I always hated the clean up involved. lately I've been using hidden studs. Are you going to have the elevation adjusting lugs on the back?

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Offline Cat Whisperer

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Cutting a spherical radius
« Reply #17 on: February 13, 2005, 12:22:12 PM »
Quote from: Powder keg
..... Are you going to have the elevation adjusting lugs on the back?  Powder Keg


It would indeed be slick if I did - because the originals did.  How to do it is the issue.  This is going to take a bit of research, thought and design time.  In the mean time I may just do a wedge or a jack.
Tim K                 www.GBOCANNONS.COM
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