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  #31  
Old Fri 07 September 2007, 06:12
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
Thanks Gerald,

If I don't ask, then I can't learn.

I'll figure something out. Maybe if I tie a couple of mules to the ....

Greg
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  #32  
Old Fri 07 September 2007, 09:44
gmessler
Just call me: Greg #15
 
Chicago IL
United States of America
Hello Gerald,
Regarding the c7 channel. I originally had C7x14.75 quoted but when I read JR's xl spreadsheet he had the C7x9.8 listed. Are there any problems with using the lighter (and thinner) channel?
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  #33  
Old Fri 07 September 2007, 10:12
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
Don't forget that the flange width is 2.090 inches versus 2.299 inches on the two channels.

I don't think it's a big issue, just needs to be accounted for.

Greg
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  #34  
Old Fri 07 September 2007, 10:25
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The lighter channel should work okay, but I have no experience of it - ours is 21 kg/m [14#/ft]
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  #35  
Old Mon 14 January 2008, 10:12
cobra427mnsi
Just call me: Paul
 
Leamington, Ontario
Canada
Hi Gerald,

I know that the 60 degree angle on the ends of the main long beams is for looks. Has anyone used a 45 degree angle instead? The reason I'm asking is I would like to get 2 pieces 123.6" long (x=100"+23.6"=123.6"), for a 50"x100" table, out of a 20'-0" channel (the standard length). A 60 degree cut will not allow 2 pcs from the 20 footer where a 45 degree angle will allow 2 pieces. If a 45 degree angle is not acceptable, I could shorten the table size to 98.5 and be able to use the 60 degree angle. What is your opinion of a 45 degree angle?

Paul
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  #36  
Old Mon 14 January 2008, 10:29
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
45 degree is 100% okay. It is also okay to have the rails overhang the main beams a bit (maybe 50mm [2"]??) - just move the last screw hole closer to the tip of the beam.
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  #37  
Old Mon 14 January 2008, 11:14
cobra427mnsi
Just call me: Paul
 
Leamington, Ontario
Canada
Thanks Gerald, for the info. You are a fantastic resource!

Paul
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  #38  
Old Mon 14 January 2008, 13:01
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
Paul,

I think you will find that the 20 foot channel will actually be longer than 20 feet. I had enough to square the ends, for a 2 inch depth, and then 45 them.

Greg
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  #39  
Old Mon 14 January 2008, 14:41
cobra427mnsi
Just call me: Paul
 
Leamington, Ontario
Canada
Thanks Gerald, that's a good idea. It will eliminate that sharp groin injuring point.

Paul
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  #40  
Old Mon 14 January 2008, 15:39
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
I would enjoy being in Gerald league, but still learning in the minors.

Greg J.
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  #41  
Old Wed 23 January 2008, 08:23
Roadkill_321
Just call me: John #7
 
Wiseton, Saskatchewan
Canada
I had a question about the X rail placement. Is there an exact measurement for this distance or is it the same distance as the thickness of the rack? How much clearance should there be between the vertical section on the main X beam and the rack?

JohnX-Rail-Placement.jpg
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  #42  
Old Wed 23 January 2008, 08:51
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
There is clearance between the rack and the beam, about 5mm [3/16"] very roughly speaking. The metric rack is 15mm wide, while the inch rack is 1/2". The rack is flush with the outside of the rail.

The clearance is left there for the guys who don't have perfect beams after welding. Right now I can't remember the exact amount, but it can not be one specific number - depends on other tolerances and rack width.
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  #43  
Old Wed 23 January 2008, 09:10
Roadkill_321
Just call me: John #7
 
Wiseton, Saskatchewan
Canada
Thanks Gerald.
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  #44  
Old Wed 23 January 2008, 18:55
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
My table measured out to plan. I have 23/32" space - evenly on both sides.
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  #45  
Old Wed 30 January 2008, 10:55
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Quote:
Originally Posted by Gerald_D View Post
The main beams, or girders, of the stationary table are made of channel iron, or C-section steel.

The most important criteria when selecting the beams at the steel supplier are not the dimensions, but the STRAIGHTNESS. Don't worry about twist,

Gerald,
What is the best way to quickly and accurately check for straightness of your beams when you get them? And how much off of perfect is acceptable?

Last edited by domino11; Wed 30 January 2008 at 10:58..
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  #46  
Old Wed 30 January 2008, 12:01
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Sighting along them with the eye is good enough. Final straightness in the rails is by shims, you just want to keep shimming to a minimum.
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  #47  
Old Fri 25 July 2008, 12:55
Marc Shlaes
Just call me: Marc
 
Cleveland, OH
United States of America
Send a message via Skype™ to Marc Shlaes
Gerald,

I have this question that I have kicked around with JR on multiple occasions.

Do you see any disadvantage to turning the main beams the other way? That way, sawdust falls right down and the hollow outside could store bits, clamps, shuttle pro and the like. Not that the storage is that important but it would me "nice".

I didn't want to do it when the time comes without asking you if it was stupid for some reason I didn't consider.

Thoughts?
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  #48  
Old Fri 25 July 2008, 13:23
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Pointing the beam out, and used for storage, could become messy. It can't be considered as clean storage, because sawdust does collect there. Table vibration could cause the goods to move and foul a passing X-motor. The table will always look cleaner with the dust collecting ledge pointing inwards.

The only reason for which I would turn the beams out, would be to run the x-motors inside the beam, inboard of belt-drives, reducing the overall width of the machine. That's one for JR to think about , but it won't work for the other axes

Other advantages of pointing the beams in:
- oversized/odd-sized boards/signs can protrude into that space.
- wide, hinging-open dust feet can protrude into that space
- clamping the rails with C/G-clamps during alignment is a lot easier
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  #49  
Old Wed 04 February 2009, 08:40
bosox79
Just call me: Derek
 
NY
United States of America
New to CNC and I have a question about the steel

Hello all,
First I would like to say that I am new to this forum and I am very excited about getting started. I have been reading and reading and reading ( and subsequently getting more excited). I talked with Joe from Alabama and will probably start by getting the laser cut parts from him. However after looking through the parts I started making a shopping list of the other parts that I would need for the frame. And so I called around to some steel mills to get quotes. The problem that I am having is with the x main beam. After converting from 21kg/m (plan 10 10 322) I came up with something roughly 31 lbs/ft, and the steel mills had nothing even close about 9-11 lbs/ft. Am I looking at this wrong? I am sorry if this is a real stupid question I am a complete amateur when it comes to steel, so this is going to be a real challenge but one I am excited to tackle.
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  #50  
Old Wed 04 February 2009, 09:08
bosox79
Just call me: Derek
 
NY
United States of America
Let me clarify

I want to clarify that I am NOT trying to go cheap, I want my build to be as close to Gerald's (structurally) as possible. I just want to make sure that my calculations are correct when going from kg/m to lbs/ft. I used and online calculator and that is where I got the roughly 31lbs/ft. I also noticed in another thread that someone mentioned that it was roughly 15lbs/ft (about half of what my calc) which is why I am confused. Also the steel the I was inquiring about was 7" x 2" which fell in the range listed in the drawings, I might have to go taller and wider to get the appropriate gauge which is fine.
Again thank you for looking.
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  #51  
Old Wed 04 February 2009, 09:16
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
1 kg = 2.2 lbs
1 meter = 3.208 ft
1 kg/m = 2.2/3.2808 = 0.670 lb/ft
21 kg/m = 21 x 0.67 = 14 lb/ft

A 7" x 2" beam at 11 lbs/ft will be fine.
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  #52  
Old Wed 04 February 2009, 09:17
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
And of course; Welcome Derek!
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  #53  
Old Wed 04 February 2009, 09:27
bosox79
Just call me: Derek
 
NY
United States of America
My Apologies

I am sorry for repeating something that was already stated (and for posting it in the wrong section). The sad thing is I remember reading all this early on and must have forgotten it or had it pushed out with all the other reading. Hopefully I will not do it again. I will have many posts as I get closer to ordering my parts. And thank you very much Gerald for all the hard work that you have put into this.
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  #54  
Old Wed 04 February 2009, 12:59
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Derek,

I know I drove Sean crazy with all the questions I asked him. We want to be sure we get the right stuff because we want our MM to be the best we can build.
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  #55  
Old Wed 04 March 2009, 08:31
SteveE
Just call me: Steve
 
Louisville, KY
United States of America
Any Issues

Gerald, I've just about completed the table assembly and am getting ready to mount the X rails and rack. I'm going the optional route by using aluminum angle with purchased V track. My question is this: since my overall table size is 5x12, is there a possibility that the weight of the gantry will cause the aluminum angle to deform? My concern is that since the entire weight of the gantry rests on the 4 V rollers, and the V track( and associated vertical leg of the aluminum X rail) overhang the main beams with no support under the vertical leg of the aluminum angle, that it might deform.
I am not so worried about the Y rails, since the weight of the car isn't as much. Am I missing something in the drawings that provide support, or am I just worrying too much.....

Steve
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  #56  
Old Wed 04 March 2009, 09:27
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The overhang is only about 5/8" to the center of the V and the alu is 1/4" thick. That is actually massively stiff (the ratio, length to thickness, is 2.5)

If you are loosing sleep over it, put the vertical screws (that hold the rail down on the beam) closer to each other, to prevent twisting between the screws.

For more peace of mind, space those screws so that both gantry wheels are not in the middle of "spaces" at the same time.
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  #57  
Old Tue 14 April 2009, 10:06
SteveE
Just call me: Steve
 
Louisville, KY
United States of America
Main Beams are bowed out.

Next problem to overcome. As I sight down the main X beams(14 feet) they are bowed outwards. haven't strung out a sight string yet, so I'm not sure exactly how much of a bow I've got, but by my seasoned eye, it looks like it's probably close to an inch of bow. I've read posts where welding was the preferred solution to pull the bow back in line. Can anyone elaborate more on this? I've never tried this technique. My welder is a Hobart handler 210, hopefully that will get hot enough to do this. Oh yea, I haven't welded on the legs or cross beams yet (actually I plan to bolt on the cross beams). Don't know if this will make a difference or not.

SteveE...
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  #58  
Old Tue 14 April 2009, 10:13
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Steve, correcting 1" of bow is not going to be easy. Are you sure it is that much?
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  #59  
Old Tue 14 April 2009, 10:38
SteveE
Just call me: Steve
 
Louisville, KY
United States of America
Bow

I'll rig up a sight line and snap a picture of it later this afternoon. Let's hope my eyesight is bad....
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  #60  
Old Tue 14 April 2009, 10:45
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
If the beams are bowing out, that means you have to shrink (shorten) the flanges pointing to the right side of the sketches below:


Welding causes shrinkage. Therefore apply welding to the parts that need to be shrunk. Suggest you start with some welds about 24" apart and then see the effect on the beam after it has cooled. You then play with the spacing and length of welds to get it into shape, but you must wait for the cooling. Welder current set to max.
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