Right Tool for the Job???

[Texasbowhunter]

I 'm in the process of attempting to fab a CNC Router table and trying to get some of the concerns I have to overcome visualized before I go that particular route...
Goal- 2 x 2 square tube needs to be fly cut on the top @ 48" long for the linear rail to fit flush...On the bottom same scenario the bottom needs to be fly cut at the ends about 4" long
My buddy has a Mill, but the table isn't long enough to do the job...The cutting portion is only about 18"...He has a table vise mounted to the table...I have in my possession 2 table vises which are matched but not matched to his...Just for reference...
I don't know how to get what I want done on his mill
So
My other buddy has a large CNC Machine very heavy-duty platform that has the platform to hold the 2" x 2" tubing and is willing to fly cut...he has never attempted anything like this...we were thinking a few thousands at a time un till we got a 1" wide or larger swart down the middle for the linear rail to sit flush......Now we have to do this twice so the finished OVAL at the upper and lower ends has to be accurate...
One thought was to get a fly cutter with a 1/2" shank since that's all he can get into the spindle
Another thought we had was to get a 1/2" end mill and make numerous passes until we get the desired finish, we are seeking...
Thought's as to other options or any one of the methods won't work and this is why or on the side of good news anyone of the afore mentioned will work and rock on...
Anyway I go, I will have to get the desired tool for the job...
I don't think It has to be dead nut accurate like your professional machinist are capable of achieving but this will be a hobbyist CNC and allot of it will be made in garage and drilled perhaps with a drill press and holes laided out by hand... so hopefully you can see where I'm going with this...
Thanks
Paul

[Bented]

Grind the rails.

You desire 0 error on your wood router correct?

A large CNC mill may have much error, it could easily be 30 or more years old.

Because something says CNC does not mean that it is accurate, merely that it is controlled.

[reggie_obe]

If the square or rectangular tube isn't straight,milling or grinding of two sides parallel will just result in a banana where any one point on face A is flat and parallel to a point on the opposite face. The linear rails are going to have to fight any bow when they are fastened to the tube. What are the steel tubes fastened to? I think you are at the machine design, not machine build stage.

[skunkworks]

2 X 2 inch 48 inches long? That seems a bit too noodly.. I would weld up a structure - then mill the areas for the linear rails...

sam

[The Artful Bodger]

I am thinking along the lines of a bedding compound.

[Paul Alciatore]

I think you are approaching this wrong. First, your linear rail is probably a lot straighter than the square tube. Second, that square tube probably has a lot of internal stress from it's manufacture. So when you machine part of it away, it will likely warp one way or another. And there goes your flat surface.

What I would do is just rough up the top surface of the square tube and the bottom of the rail. Be careful while doing this to the rail as you do not want to bend it. I would work holding it by hand and on a four or five inch section at a time. Also do any other machining operations on the square tube before the next step, which is stress relief. Place the tube outside in a hot spot where the sun can hit it and leave it there for two or three days. Flip it over at least once. The heat/cool cycles should relieve much of those residual stresses. You could do this in an oven if you have one that is big enough.

Then get some slow hardening epoxy (JB Weld is a good one), mix it, and apply a generous amount to the top of the tube and bottom of the rail. Then gently place the rail on the tube and let gravity do the final placement. Don't force it down and don't use weights. Leave it undisturbed overnight. Clean up any excess epoxy after it cures.

Your rail should remain straight and be firmly attached to the tube. Make any adjustments of the track's position by shimming or sideways motion on the mounting bolts.

One more thing; if you are a welder, LOCK UP ALL YOUR WELDING EQUIPMENT (AKA STRESS MAKERS) until this project is over. Use bolts and nuts for fastening things together. Add gusset plates if needed. Don't run a bolt all the way through the square tube:that will distort the tube. Just fasten to one side of it. Tap the holes if you can not reach the inside of the tube to place nuts. Pop or blind rivets may also be a good fastener to use.

[jcge]

Maybe weld mounting pads on and then machine those rather than the tube.

[RMinMN]

While wishing for perfect accuracy is an admirable goal, your router will be cutting wood and getting wood cut to within .002" for any length is possible but it won't stay that way as wood will move much more than metal. For your linear rails, don't try to machine the tube full length. Use high-spot blue on the linear rail to indicate where it touches the tube. Sand down the high spot and test it again. You'll be less likely to make the tubing into a weird shape that way.

[reggie_obe]

Do any of the manufacturers of square or round tube make any claims for straightness?
80/20 Aluminum extrusion is probably a better starting point.

[Texasbowhunter]

Grind the rails...this is an approach I had not considered...

If the square or rectangular tube isn't straight, milling or grinding of two sides parallel will just result in a banana where any one point on face A is flat and parallel to a point on the opposite face. The linear rails are going to have to fight any bow when they are fastened to the tube. What are the steel tubes fastened to? I think you are at the machine design, not machine build stage.
I can sort of see this happening

I am thinking along the lines of a bedding compound. Yes What would you use?


I think you are approaching this wrong. First, your linear rail is probably a lot straighter than the square tube. Agreed 100%
Second, that square tube probably has a lot of internal stress from its manufacture. So, when you machine part of it away, it will likely warp one way or another. And there goes your flat surface.
Consensus by allot of you guys that do this for a living...

What I would do is just rough up the top surface of the square tube and the bottom of the rail. Be careful while doing this to the rail as you do not want to bend it. I would work holding it by hand and on a four- or five-inch section at a time. Also do any other machining operations on the square tube before the next step, which is stress relief. Place the tube outside in a hot spot where the sun can hit it and leave it there for two or three days. Flip it over at least once. The heat/cool cycles should relieve much of those residual stresses. You could do this in an oven if you have one that is big enough.

Then get some slow hardening epoxy (JB Weld is a good one), mix it, and apply a generous amount to the top of the tube and bottom of the rail. Then gently place the rail on the tube and let gravity do the final placement. Don't force it down and don't use weights. Leave it undisturbed overnight. Clean up any excess epoxy after it cures.

Your rail should remain straight and be firmly attached to the tube. Make any adjustments of the track's position by shimming or sideways motion on the mounting bolts.
YES this has been a consideration I have thought about doing...

One more thing; if you are a welder,
And I'm not a welder But a novice welder still learning
LOCK UP ALL YOUR WELDING EQUIPMENT (AKA STRESS MAKERS) until this project is over. Agreed
Use bolts and nuts for fastening things together. Add gusset plates if needed. Don't run a bolt all the way through the square tube that will distort the tube. Just fasten to one side of it. Tap the holes if you cannot reach the inside of the tube to place nuts. Pop or blind rivets may also be a good fastener to use.

Do any of the manufacturers of square or round tube make any claims for straightness?
It's certainly possible but I have not seen it in my limited material I have available to me...
80/20 Aluminum extrusion is probably a better starting point.
Using this "T: Slot extrusion would certainly make life easier for me and I have seen allot a unit out there that has used this Extrusion successfully and am considering using it if all else fails, now with that said there are those that have stated the usage of this material is not suggested when building a unit that will be able to machine aluminum which is a goal I HOPE to achieve...Note: On occasion will it be used for aluminum, however its primary use will be wood and such...I also understand that I can't expect it to hog out a swarth of material .10 x ,20 deep... but if I can get it done with perhaps cutting a depth of .050 deep slowly I believe I'd be content...

Now with all this conversation My mind is going into overdrive and I believe now I will forgo this attempt to surface the entire linear rail area and lean towards some type of liquid material a (epoxy/resin based) and allow it to be the bed for the rail to mount upon...JB Weld has been suggested and I have used this on projects, and it certainly seems to be adequate for the desire affect I have used it for...Is there something better that is attainable to the public?
So, along this line of progress what If I was to create a foundation on the entire surface of the tube where the rail would sit upon, allow to cure creating a new foundation...Then after the material epoxy/resin or ? cured then had the new material surface fly cut or machine with perhaps an end mill to create a fresh machined surface out of the epoxy/resin for the rail to sit upon...
It's along the lines of what Paul suggested but has a twist...Thoughts here would be for lateral adjustment in fine tuning the rails to be equal to each other and would allow (at least in my feeble thinking) a solid foundation under all the base of the rail...
I can do this on the CNC machine my bud has...The material would be relatively easy to move and get a nice foundation for the rail...
Thoughts?
Great Input...This is why I like to spit ball with you guys as much as I do...You get the creative juices flowing...And for this I am Grateful...
Thanks
Paul

[The Artful Bodger]

Unfortunately I am not familiar with what may be available as a bedding compound in Texas but Paul A suggests JB Weld.

[Bented]

For farks sake do not try to build a sub .0005" accuracy machine from commercial components, this will end in tears.

I understand that you would like a wood router that resolves to several individual .001" increments.

Do not however lose your head.

This leads to madness.

[deltap]

Another approach would be to shim the rail or use leveling screws.

[darryl]

I agree with all the suggestions about not machining the tubing. And I think your linear rails would be straighter than the result you could get by milling- even if you could machine the 48 inch length, even a good machine is unlikely to give you a greater accuracy than a proper linear rail.

If you can avail yourself of a surface plate of suitable length, you can jig up the structure to allow the closest fitment of parts while the bedding compound sets. I'd use JB for that- it does give a strong bond, plus it has a long enough setting time that you won't necessarily encounter a problem in using it. For the square tubing, do all machining operations on it first- drilling, tapping welding on of tabs, etc- before you commit to the bedding operation. If this is going to be a welded up frame that you can subsequently set down on the linear rails which are positioned on a surface plate, you are then likely to achieve a useable accuracy. Of course you don't want to force the framework into contact with the rails- you want it to just settle into the JB with whatever level of warpage it already has. It's going to touch down on the rails at some points, and leave gaps at others- the end result is rails straight and parallel, not a framework that's perfect.

You might even consider another steel size- say 1-1/2 by 3 instead of 2 by 2 so you could use the steel in its stiffest orientation.

Here's something else I learned about using JB weld as a filler and bedding compound- you can always drill and tap for placement of holding bolts after the JB has set if you're worried about parts coming apart. Don't add the bolts in while the JB is soft- you'll just introduce stresses and twists that you're trying to not have in the first place. Put the bolts in later, and they don't have to be 'smokin tight'.

[psomero]

Grind the rails...this is an approach I had not considered...

If the square or rectangular tube isn't straight, milling or grinding of two sides parallel will just result in a banana where any one point on face A is flat and parallel to a point on the opposite face. The linear rails are going to have to fight any bow when they are fastened to the tube. What are the steel tubes fastened to? I think you are at the machine design, not machine build stage.
I can sort of see this happening

I am thinking along the lines of a bedding compound. Yes What would you use?


I think you are approaching this wrong. First, your linear rail is probably a lot straighter than the square tube. Agreed 100%
Second, that square tube probably has a lot of internal stress from its manufacture. So, when you machine part of it away, it will likely warp one way or another. And there goes your flat surface.
Consensus by allot of you guys that do this for a living...

What I would do is just rough up the top surface of the square tube and the bottom of the rail. Be careful while doing this to the rail as you do not want to bend it. I would work holding it by hand and on a four- or five-inch section at a time. Also do any other machining operations on the square tube before the next step, which is stress relief. Place the tube outside in a hot spot where the sun can hit it and leave it there for two or three days. Flip it over at least once. The heat/cool cycles should relieve much of those residual stresses. You could do this in an oven if you have one that is big enough.

Then get some slow hardening epoxy (JB Weld is a good one), mix it, and apply a generous amount to the top of the tube and bottom of the rail. Then gently place the rail on the tube and let gravity do the final placement. Don't force it down and don't use weights. Leave it undisturbed overnight. Clean up any excess epoxy after it cures.

Your rail should remain straight and be firmly attached to the tube. Make any adjustments of the track's position by shimming or sideways motion on the mounting bolts.
YES this has been a consideration I have thought about doing...

One more thing; if you are a welder,
And I'm not a welder But a novice welder still learning
LOCK UP ALL YOUR WELDING EQUIPMENT (AKA STRESS MAKERS) until this project is over. Agreed
Use bolts and nuts for fastening things together. Add gusset plates if needed. Don't run a bolt all the way through the square tube that will distort the tube. Just fasten to one side of it. Tap the holes if you cannot reach the inside of the tube to place nuts. Pop or blind rivets may also be a good fastener to use.

Do any of the manufacturers of square or round tube make any claims for straightness?
It's certainly possible but I have not seen it in my limited material I have available to me...
80/20 Aluminum extrusion is probably a better starting point.
Using this "T: Slot extrusion would certainly make life easier for me and I have seen allot a unit out there that has used this Extrusion successfully and am considering using it if all else fails, now with that said there are those that have stated the usage of this material is not suggested when building a unit that will be able to machine aluminum which is a goal I HOPE to achieve...Note: On occasion will it be used for aluminum, however its primary use will be wood and such...I also understand that I can't expect it to hog out a swarth of material .10 x ,20 deep... but if I can get it done with perhaps cutting a depth of .050 deep slowly I believe I'd be content...

Now with all this conversation My mind is going into overdrive and I believe now I will forgo this attempt to surface the entire linear rail area and lean towards some type of liquid material a (epoxy/resin based) and allow it to be the bed for the rail to mount upon...JB Weld has been suggested and I have used this on projects, and it certainly seems to be adequate for the desire affect I have used it for...Is there something better that is attainable to the public?
So, along this line of progress what If I was to create a foundation on the entire surface of the tube where the rail would sit upon, allow to cure creating a new foundation...Then after the material epoxy/resin or ? cured then had the new material surface fly cut or machine with perhaps an end mill to create a fresh machined surface out of the epoxy/resin for the rail to sit upon...
It's along the lines of what Paul suggested but has a twist...Thoughts here would be for lateral adjustment in fine tuning the rails to be equal to each other and would allow (at least in my feeble thinking) a solid foundation under all the base of the rail...
I can do this on the CNC machine my bud has...The material would be relatively easy to move and get a nice foundation for the rail...
Thoughts?
Great Input...This is why I like to spit ball with you guys as much as I do...You get the creative juices flowing...And for this I am Grateful...
Thanks
Paul

Only read part about 8020, too lazy to erase superfluous quotation.


8020 ain't flat or straight and they are very reluctant to disclose their tolerances for both parameters. If you want good straight extrusion you're better off with Parker IPS, Item, Bosch or Paletti.

Many extrusion profiles have slightly angled wings thay are not parallel and get deflected when you tighten a t-nut, also. If you're looking to put a linear rail on top of a "flat" surface, plain 8020 is certainly not the thing you seek.