Hi, thanks for the info here. BTW, the inconsistency didn't come from the cutting, they cut initially within .4mm, but since one rail was off to the other, I thought sanding it down would work. Perhaps the disc expands when hot or something changes. Well, I suppose I learned the lesson the hard way. I'm just curious if I can somehow salvage this, as it would cost me $200 more in angle iron to recut them, not to mention the couple more days.

My X length rail total is 4500mm,
1 X rail is sitting good at 27.5mm to 28.45mm
other X rail is sitting at 26mm first quarter to 28mm
My Y length rail is 1950mm,
Both Y rails are at 26mm +/- .5mm

Does anyone know if it would present any problems to have the rails at 24mm high rather than 28mm, and use 4mm flatbar to shim them up with?

Thanks for the info on the methods everyone. I'll definitely use a better method.

Cheers,
Chris

Ok salvage it is.

There is no harm in making the rails and checking the fits yourself with out any packers. If necessary put in some packers should problems arise..

Some tolerances will change regardless.
1. the gantry / Y axis car will move towards the top of the rail
2. the swing plate mounted to the gantry / Y axis car will move away from the rail

Ross

The drawings used to show 25mm rails and they did work sort of okay.....

- The skate rollers need to miss the curved fillet inside the corner of the angle iron.
- When using small pinion gears the motor shafts can foul on the gantry ends
- the slots in the motor plates don't allow the motors to swing that far up

Thanks for chiming in Gerald. What if I place a 10 x 3mm flatbar shim under the rack? Will that space the swing plate far enough back into position ok? Suppose I could order more angle iron later on if this doesn't work... Not much to lose trying at this point.

BTW< what is everyone using to check the rail height across the entire rail? Gauges? I've been using my calipers and square.

A spacer under the rack is more trouble than solving the other implications will be. Simplest is a pinion size just bigger than minimum (if you plan on belts/gears anyway.). Otherwise a bit of local filing/grinding will get the motor plates swinging further up.

Thanks Gerald.

I have one X rail that teeters between 28.00 and 29.34. Am reticent to sand it further down in case I mess it up. Perhaps will just lightly sand the areas that are too high.

Out of the bad X rail, I can cut a segment out that would be 28mm long for one of the Y rails 2000mm long.

Which leaves me to only have to purchase one more 6m long piece of rail for $60 NZD. What I'm wondering is, would it be ok to weld together 2 pieces of angle iron to create a single Y rail 2000mm long for the other X rail, one piece would be 1500mm, and the other 500mm? Then cut and bevel that one down to 28mm as one piece? If this is the case, then this mistake would only have cost me $60.

Also, one other question, can I use M10 stainless bolts on the rail skate for height adjustment, instead of M12, as this will save me $40 in tap, 13/32 drill bit, and setscrew/nuts. The hole on the rail skate taps fine at M10, so was just wondering as this would reduce my mistake down to $20 (minus a few days work) while keeping a 28mm rail height.

Many thanks for all the help guys, She's coming along. Should have the table, gantry, and Y car finished early next week but not painted. Will redo the rails on the built table instead of on the ground.

Cheers,
Chris

Sand down the high parts :eek:

No way ... deck the whole rail to a single height with a series of continuous actions along the whole length of the rail.
The high parts will get touched while the low parts will be left alone.
The final pass will lightly touch all of the rail ensuring a consistent height.

i'll leave the rest to someone else.

Regards
Ross

That is what I was trying to do with the other rails which brought them down to 25-26mm. Something must be wrong with my grinder when it gets hot. It's a bosch too.

Could you show us a few pics of how you did it and or the jig you used.

Ross

Sure, just used the skate in the plans. Leveled out the bolts with a square and digital calipers. I used a sanding disc on top of a grinding disc. Will post photos when I get back to the shop next week.

Chris

This is no mystery, carefully study the attached photo with me.

Attachment 13725

By just using four bolts, no matter how carefully measured for height, error creeps into the process.
The reason for this is that the bolts are very close to the disk itself.
They are clearly visible in this shot.

This jig provides an very large flat surface that controls any movement both left to right and back to front.

Also note that I have two melamine surfaces sliding over the top of each other.
This is to minimise the friction on the surfaces so that thay slide with a smooth action.

Looking at the pics of the rails you posted you have not been able to control some of the the front to back movement with just the four bolts sticking out of the top plate of the skate.
Hardly a surprise as the aspect ratio of the height of the bolts to the width is working against you.

By comparison the jig I have used supports the grinder over at least 3 times the distance front to back, let alone any calculation of the total surface area the jig bears upon.

PRACTICE

The next step is to make a jig, then practice on something non critical.
I know that sounds a obvious but so many rip into expensive materials with no previous experience then wonder why something has gone wrong.
That is exactly why those smug tradesmen with their lifetimes of experience laugh at a newbies trying to emulate their skill.

Good luck with your rails, you now know everything you need to know !!

Regards
Ross

Thanks Ross, I'll definitely make that jig and use it on the rails once I get the table up. I'm going to shift on getting the table up next week so I can have a higher surface to work on. Then I'll get the melamine boards to make the jig.

Thanks again for the tips.
Christian

http://www.mechmate.com/forums/showt...0&postcount=29

Previous production version of same idea....
Notice plastic PVC laminate on bottom of plywood sled for gliding

You dont seem to mention a cutting disk, are you using a cutting disk to cut the angle to the correct height or are you grinding it down with the sanding disk/grinder combo?

Found a great article on how to heat straighten beams without welding them, just with a torch. http://www.fhwa.dot.gov/bridge/steel/02.cfm#d. Going to try it tomorrow in my beams.

Actually, both are the same thing. I find welding is the easier way to apply heat...

Chris great detail there.

Ross

It's a good paper on bending beams with heat, knowing any beam can be straightened with this method is a relief. Plus, I don't have to weld, or grind them out later. Should be interesting. I will try using the V method on my beams and my rails which have slightly bent.

Will continue with cutting rails later in the week.

Just a question about the support board. At the moment, I can get 2x 12mm 3660 x 1800 mdf. Can I glue those together for the support board material?

Thx

Chris

I'd say it's not a problem. I would use epoxy for glue.

You get to do this again when you glue the sacrificial layer on after bolting the base board to the frame.

PS there are some good suggestions in the forums about drilling through both sides of the base board cross supports so you can easily drill the base board, and for clamping the base board under the supports when drilling so that you get to work from above, rather than getting sawdust in your eyes, like I did.

Hey Red, thanks for the advice. I did drill straight through my cross channels for a vacuum plenum later on, so now I know to clamp the board to it and drill through in order to get it drilled. Thanks!

Chris

Help,
Having no luck with bending one of my large beams into place. I heated one of them straight, then the other one over compensated and I haven't been able to get it back.. Can anyone tell me how to weld a beam straight that is bent on the webbing side, not the flange side? Ie opposite to how it is bent in the illustration that Gerald made please?

Thanks
Chris

Applying correct amount of heat with torch is way above me. Hence, welding is my prefered heat source which I can gauge the heat to a very close ball park.
I can't offer much help on the correct way to do your straightening job, also, I really don't understand what you want. a sketch would be really helpful.
For now, all I can tell you is that metal will string towards the side where you apply the heat. i.e. the heated spot will become the inside of a bow. (if the beam started out as a perfectly straight piece; I get confuse with bow-in & bow-out... :o)

Here is a pic of the bend with explanation. I've tried that but it just became worse. Not sure why.

http://i45.tinypic.com/etrwu8.jpg

Can't quite make out the text on your image. I believe that you are indicating how it is bowed, not how you want to bend it. The method that Gerald described in the thread you mentioned is probably the best. I did not have to do this on my main beams, and have not had to do this with any channel as heavy or large, but it should work. I would start in the center of the bow, make the welds, let them cool and check for any change. If it has improved at all, I would work out towards the ends about every 24 inches as Gerald recommends. How bad is the bow? You may be able to compensate and straighten when welding on the supports.

http://www.darkforrest.com/gallery2/...serialNumber=1

Ted

Great, thanks for the advice. I'll give it a go. Shall I weld just on the bottom flange or both bottom and top, and do I just weld on the inside?

It's bowed about 8mm, but it was only 4mm till I started heating it.
Thanks,
Chris

When I have done this on lighter gauge and smaller channel (for trailers), I did both flanges, only on the inside, to try and keep out any twist. You will need a lot of heat. Here is a link that may help explain heat straightening in general. In particular, check out Fig.5.

http://www.metalwebnews.com/howto/co...ntraction.html

Ted

Well, I have nearly finished tack welding the table up. As shown. I gave up on trying to straighten the beam with heat as it simply will not straighten this way. I figured I'd try to install the cross braces then straighten it with an all thread clamp while heating it up, then tighten all the cross members and tack weld them. Anyone else use this technique? As you can see, the dimension is suppose to be 1980 all the way accross, and it is either short in the middle, or long at the ends.

Still a bit of structure to weld on this massive table. Not sure how I will turn it over without 10 guys:) I used bolts on the cross brace frames so i could take it apart if need be, then turn it over.

[IMG]http://s21.postimage.org/4375gqxx3/IMG_2003_1.jpg
pic upload[/IMG]

More progress on frame. Need to drill holes on webbing for the all thread clamp to get it to straighten out prior to welding the legs on. I'm also thinking of loosening the cross frames up where the gaps between the main X beams are too long, then welding the legs on where they are supposed to be on the beams, then tightening the cross frames to the legs hopefully pulling the beams straight. Welds are for the most part clean, except for a few that were difficult to get to. The argoshield makes a night and day difference to flux core any day.

[IMG]http://i47.tinypic.com/2lvmmxk.jpg[/IMG]

That's big stuff
 

Looking good.
That's some heavy looking metal there.
Nice stuff.
Cheers
Andrew

Thanks, it is pretty heavy, that is for sure!

Here is how I managed to correct the beam that was crooked. I use the allthread to pull them together, then I lifted them and hammered in the bottom.

http://i46.tinypic.com/2lboswj.jpg

And on the inside to spread them apart:

http://i49.tinypic.com/x4etr5.jpg

I'm hoping that this didn't cause any more problems, i.e. twisting, or anything like that. It seems as if my flanges are becoming a bit bent with all the weight on them now.

http://i46.tinypic.com/23ijw2s.jpg

...love a good trolley jack!

What would I do with the trolly jack Sean? Is that how I should turn it over?

I have 3 mdf boards, each 12mm thick, can I get away well enough with 2x for the support board, and 1 for the spoiler lard, or should I glue all 3 together for the support?

1 support and 1 spoil board will do it.

It will be quite flexible if I use only 1-12mm board as support, won't it?

We usually use a 30mm board as the support and 22mm as sacrificial surface. If you want to use whats on hand, glue two 12mm board together, mount them to the table with the counterbored holes as per usual, fix to the table and glue the last 12mm board on top, you wont get the same working life from you sacrificial board but at least you can start working.

great, I liquid nailed the support boards together. Should be ok. Turned the table over today, all going well. Going to start priming it tomorrow.

Here are some primed bits, going to rust converter the main table prior to priming with a 2k primer..




http://i49.tinypic.com/1z3yyj4.jpg

Resuming the Rail Cutting Adventure
 

Ok, back on the rails now that I have a flat surface to work on. Built the jig for the rail grinding, per Ross' rig. Used 300mm x300mm Melamine about 16mm thick x2. Did a test and it worked out so much better. On the test rail, I was only off by .2mm across apprx 1.2m stick from 28.25mm to 28.45ish mm. Hoping that is going to be acceptable on the big pieces.

A note: I upgraded to 125mm Pferd Discs as they were only .30c more ea for 10mm extra material. Seems to be worthwhile and they smell just as good as the smaller ones (love the smell of pferd discs burning in the morning:D ). They fit my Bosch 115mm grinder post so I figured what the hey. I also purchased some F clamps, which seem to do a heck of a better job than the old plastic clamps I had around.

Also, made heaps of progress on the rest of the table, and now switching into electronics mode, and working on the Zslide. I'm going to get everything rolling on rails before I paint over the primer incase I need to rip into something to straighten it out as the x beams still are on perfectly level or straight, though they are much closer now. What a headache it was fixing messed up 180pfc beams. No matter what the guy says, next time I won't take delivery on the beams if they are mucked up as it will cost triple in gas and time just to straighten them out.

Here are some pics.

http://s16.postimg.org/ok37l5aol/IMG_2065.jpg

http://s16.postimg.org/6ik2ncgnp/IMG_2067.jpg

http://s16.postimg.org/6wlemy0r9/IMG_2069.jpg

http://s16.postimg.org/92fphg47p/IMG_2071.jpg

http://s16.postimg.org/ymhznvplh/IMG_2073.jpg

http://s16.postimg.org/jf203ixqt/IMG_2077.jpg

http://s16.postimg.org/wx8wft9w5/IMG_2079.jpg

http://s21.postimg.org/eei9m3mmv/IMG_2061.jpg