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  #61  
Old Wed 15 April 2009, 07:44
SteveE
Just call me: Steve
 
Louisville, KY
United States of America
Here's a snapshot of the bow. Sorry that the focus isn't better


I should mention that the string is on the opened side of the C channel.

The bow looks to be about 1/2 to 5/8 at the middle.


SteveE
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  #62  
Old Wed 15 April 2009, 07:54
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Okay, that bow is opposite to what I first thought. 5/8" over 14ft sounds reasonable. Will make another sketch when I get home from the commute that is starting in 5 minutes.

(That beam is not supposed to be drilled & tapped yet - we can't promise to get all the holes in a straight line )
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  #63  
Old Wed 15 April 2009, 07:59
SteveE
Just call me: Steve
 
Louisville, KY
United States of America
Double drat!!

I have a tendency to jump in before I check the water a lot of times!!!!

One of these days, I'm going to learn to write down all the steps needed in project in the order they need to be performed in, and then follow it!

SteveE.
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  #64  
Old Wed 15 April 2009, 10:13
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
This will make it curve the other way:


Again I suggest you start at 24" intervals. To make a nice straight weld, run the gas nozzle against a bit of scrap used as a straight-edge.

Don't worry about the holes at this stage. You could enlarge them later and put washers & nuts below. (If the oversized holes in the rails don't give enough tolerance)

The bolted/welded cross-supports will also help tremendously to hold the beams straight.
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  #65  
Old Wed 15 April 2009, 12:45
SteveE
Just call me: Steve
 
Louisville, KY
United States of America
Bow

Gerald, last couple of questions before I fire up the welder.

1) Is it better to start in the middle of the beam and work my way out to the ends, or does it not make a difference?

2) After all is straight, true and cooled down, can I go back and grind the welds down smooth. Or will that just let the beam bow again?


Thanks for the input and help!!!

SteveE
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  #66  
Old Wed 15 April 2009, 13:03
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
It doesn't matter where you start, but you see results quicker if you start in the middle. Grinding the welds will relax them very slightly and re-introduce a little of the original bow.
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  #67  
Old Thu 23 April 2009, 09:02
SteveE
Just call me: Steve
 
Louisville, KY
United States of America
Double drat!!!

Just a note for those that are in the planning stages and have not yet purchased steel. When you find a supplier of the large C channel, be sure to check for the squareness of the channel before purchasing. I purchased 2 20' channels to get the 2 14' rails I needed. After all welding and drilling I discovered that one of the channels was not even close to square(flanges were not parallel to each other nor were the flanges perpendicular to the face of the channel), while the other was perfect. I contacted my supplier and found out that they normally purchase from American Steel, but just prior to my delivery they got in a shippment from an import supplier. So my order was mixed. So let my woe's be a word of warning........ By the way, it was the import steel that was way out of square...... On a good note though, my supplier is replacing the bad channel for free, just my time and effort lost....

SteveE
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  #68  
Old Sun 24 May 2009, 03:10
cvriv.charles
Just call me: charles
 
New Jersey
United States of America
I was researching steel channel online. I ran across this one site that listed the channel size like this: (7" x 12.25#). I'm assuming that 7" is the height. What is the 12.25#?
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  #69  
Old Sun 24 May 2009, 03:56
MattyZee
Just call me: Matt
 
Adelaide
Australia
it refers to the weight of the beams. 12.25lb (#=pound) per foot. I think the drawings state ~21kg/m which is ~ 14.1lb/ft. I don't think the couple of pound variation will make much difference...
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  #70  
Old Sun 24 May 2009, 04:57
cvriv.charles
Just call me: charles
 
New Jersey
United States of America
@ Steve - Your problem totally answered my question about purchasing really long beams like this. I was assuming that the longer the beam the greater the chance it would be out of whack. How do you check out he material before buying?!?! I was going to purchase what I need online or maybe call them up over the phone and explain to them the importance of straightness with my order.

I found a place discountsteel.com where I will probably purchase my material. I can buy pretty much exactely what I need size wise. I can buy the main x beams in several sizes. In my situation, two 7" x 12.25# x 11' beams for 268 without shipping and tax.

I actually found out about the 12.25# thing. My cad software gave me the specs for it. I just dont know how all that was derived from 12.25#. About the x rails,... I was thinking about using .375" unequal angle for my rails. The v-groove bearings would have more of a surface to roll on maye lengthening the life of the rails?!?! What do you think?
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  #71  
Old Sun 24 May 2009, 04:58
cvriv.charles
Just call me: charles
 
New Jersey
United States of America
Oh ok,... thats fine. I'll get the 14.74 if thats what the plans call for. I need this router to be rock solid.
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  #72  
Old Wed 15 July 2009, 13:00
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Gerald,
I found one thread where someone used bent up c channel for the table cross bearers and main beam. You didnt seem to have any objections to that at the time. Do you see any downside to doing this? I am pricing some steel for my table and my supplier, who also does my bending for the laser cut parts, said he could bend me up any size I needed cheaper. They are a little slow in work right now so it would be cheap.

If the bent channel is ok do you have any recommendations for plate thickness etc?

The main reason I am entertaining this is I am thinking of having a larger height than stock for 3D work and the larger beams add up in weight rather quickly.
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  #73  
Old Wed 15 July 2009, 13:35
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Heath,
Knowing what I know about cutting 3D stuff. I would recommend using the 8" channel and then building a spacer or step down frame for the extra depth. This would put your cross bearers lower in the z direction.
This has already been done on one MM recently.

For routine work, you can have a "boxed out wooden or mdf" riser in place that if done well, could double as a vacuum plenum.

Just my 2 cents.

Sean
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  #74  
Old Wed 15 July 2009, 21:51
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Heath, are you thinking in terms of bending up one wide C-channel instead of bolting together two narrower ones? How tall do you want to go?

(PS. it would help if you could point me that other discussion to refresh my head)
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  #75  
Old Thu 16 July 2009, 07:00
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Gerald,
I was thinking of going in the 10 to 12 inch range for the main beam. My bender, who is probably going to supply my steel as well, suggested he could bend me some beams more economically than buying the standard channel. Also I was looking in some tables and for the 12 inch beams they get pretty heavy real fast. The smallest lbs/ft was 20.5.

The thread was Ries in Equador.
http://www.mechmate.com/forums/showt...4&postcount=22
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  #76  
Old Thu 16 July 2009, 09:32
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by domino11 View Post
. . You didnt seem to have any objections to that at the time. . . .
. . . . his beams were a fait accompli, so I decided rather to just keep quiet.

As an absolute minimum, I would pick 6mm thick, but 5/16" or 3/8" would be better.

Few bending companies will bend that accurately over 3m. Their tools are typically worn in the middle and the frame of their bender will flex at the huge tonnage required. Typically, the ends of your channel will be bent 93 degrees while the center part is only bent 87 degrees.

And then you must realise that plate of that thickness will have an outer bend radius of more than 1/2". That means your angle rail will have at least 1/2" less support.
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  #77  
Old Thu 16 July 2009, 09:49
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Gerald,
So, I will ask the question. Would it be more accurate in this situation to use a 5/16 or 3/8 HRS flat bar and control your stitch welding and setup?
It's a lot more work, but feasible if the Section modulus/centroid/bending numbers worked out for the new made up section.
You still have the issue of unsupported rail in my picture below, albeit only 3/8" The angle section could be moved inboard, but that brings up the challenge of structural members and angle of the flanges, etc.

Picture below show with 3x3x5/16 angle and 3/8 x 12" HRS flat bar. Overall height as shown is 12-3/4" face to face

section_beam.JPG

Last edited by smreish; Thu 16 July 2009 at 10:07..
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  #78  
Old Thu 16 July 2009, 10:13
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I would rather start investigating rectangular box tubing (maybe a stacked pair) before trying to weld an angle iron in a straight line.

(The flanges of a channel beam are always thicker than the web)

Also if one goes to a wide channel (tall) then it should start getting vertical ribs.
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  #79  
Old Thu 16 July 2009, 12:13
KenC
Just call me: Ken
 
Klang
Malaysia
Welding on angle iron longitudinally is the best recipy to make it cure (violently) What about using I-Beam or H-section? They are nrmally heavier and more stable in shape.
Trim off excess pertrusion under the rail angle using the Skate. Do you think it will work?
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  #80  
Old Thu 16 July 2009, 17:08
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Gerald,

I like the idea of rectangular tubing. Since I have problems with my C Channel, I thought it would be another way to go.
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  #81  
Old Thu 16 July 2009, 22:46
buibui
Just call me: John #34
 
Seattle
United States of America
Quote:
Originally Posted by KenC View Post
What about using I-Beam or H-section? They are nrmally heavier and more stable in shape.
Trim off excess pertrusion under the rail angle using the Skate. Do you think it will work?
Ken, an i-beam will work and is what I used in my build. I notched the excess the way you describe, except with a jigsaw and metal cutting blade. This was really just for aesthetics though, and an overhang would work the same.

Of course, I realize this doesn't solve Heath's problem, as weight adds up with i-beams as well.

006.JPG
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  #82  
Old Thu 16 July 2009, 23:22
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
We must understand clearly that the more weight we have in these beams, the better. When we engrave small signs at high speed, even the heaviest of our tables start to dance.
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  #83  
Old Fri 17 July 2009, 07:11
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Thanks all for the input,

Gerald, yes I understand the benefits of added mass in the table structure, but was concerned on the handling of the parts. Maybe I just have to get more beer for the helpers I will need to erect the table.

My initial interest in some added Z clearance was for smallist 3D stuff and a small indexer. I think I will entertain a drop table arrangement as Sean suggested for anything larger later on.
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  #84  
Old Fri 17 July 2009, 08:50
Doug_Ford
Just call me: Doug #3
 
Conway (Arkansas)
United States of America
That's some beautiful work John. Really clean and professional.
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  #85  
Old Sat 18 July 2009, 09:47
KenC
Just call me: Ken
 
Klang
Malaysia
John, beautiful work there!

What size I beam did you used? If I can source suitable H-section, I will screw the angle flash to the beam edge and glue the ract direct on the beam. More Structural stability and less work

I won't worry about bulking and bowing in the case of the C-channel.

BTW, what did you coat the rail with? Looks professional! I like.

Last edited by KenC; Sat 18 July 2009 at 09:58..
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  #86  
Old Sat 18 July 2009, 10:25
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by KenC View Post
I will screw the angle flash to the beam edge and glue the ract direct on the beam. More Structural stability and less work
and your motors won't drop down far enough.
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  #87  
Old Sun 19 July 2009, 00:42
buibui
Just call me: John #34
 
Seattle
United States of America
Doug and Ken, thank you. I hope to have more updates this weekend.

Ken, my beam is 8" x 4" and 18.5 pounds/foot. The finish on the rails is just black Rustoleum spray paint, and the blue is a polyurethane paint (imron).

As Gerald mentioned, the motor may not reach if the rack is mounted directly to the beam. But also keep in mind that the flange of the beam may be tapered (such as mine) and the rack would not sit flat and mesh with the pinion properly.
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  #88  
Old Mon 20 July 2009, 06:30
KenC
Just call me: Ken
 
Klang
Malaysia
Gerald, John,
Thanks for the info and advise, will follow suit. I'll look out for the 4"x8" I-beam, 18.5 lb/ft=101.33kg/m? Very heavy! is that correct? I read from my table that there is a 178x102x21.54kg/m I beam should improve the rigidity significantly without the weight penalty..

I recon with the 4"x8" I beam will also increase the effective Z-travel by 1"? with minimum lost of Z-axis rigidity?

Last edited by KenC; Mon 20 July 2009 at 06:39..
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  #89  
Old Mon 20 July 2009, 06:48
KenC
Just call me: Ken
 
Klang
Malaysia
My mistake, 18.5ib/ft=27.27kg/m.

Shouldn't have huge cost different.
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  #90  
Old Sat 23 January 2010, 08:26
swatkins
Just call me: Steve
 
Houston
United States of America
Quote:
Originally Posted by chris saintdenis View Post
If have come across some used free C-channel for my main long beams, but the problem is the upper and lower surface are not running parallel to one and other. One side is about 1mm out of square with the outside long edge of the c section and the other side is 3.5mm out of square.

Looking at the construction of the Mechmate it seems critical that these surfaces run parallel. I include pictures because I am sure the above explanation is not all that helpful. Any thoughts?

Thanks for your time.
I have run into a similar problem.. My channel is made with a tapered flange. When I hold a square with one leg on the flange and the other on the side of the beam I see a void of about 1/8", the outside edge of the flange is lower than where the flange attaches to the beam.. The beam is in otherwise good shape and I am trying to keep costs low so I was thinking about shaping the profile of the flange by removing the High edge of the material...

Has anyone ever tried to modify the skate so that it could be used to grind the top edge of the Beam?

I have not cut my 20' long 8' wide channel into the two beams yet so this is the time to correct the problem..

I was thinking about placing the beam on saw horses with the flanges facing down. That would give me a wide flat surface for a modified skate to rest against. I need some way to keep the two flanges parallel and the grind depth equal so I was thinking of making a fixture that would allow the grinding plate to be held at a 90 degree angle to the flat portion on the beam and having a gauge roller ride along the opposite flange to control the depth of the grind..

To use this fixture I would place it on the beam's wide side, adjust the roller gauge so it would take a light grind, and push the grinder to the other end of the beam.. Then I would adjust the roller gauge so that the grinder would take another light grind and push the grinder along the opposite side thus flattening it also... By alternating the sides I should be able to square up the corners and grind the beams evenly...


Think this will work?
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