DIY Linear Rails

[JerryFlyGuy]

Ok, onto my next linear rail question. Assume that I'm going to purchase some pretty good size rails and shouldn't need to do to many joints per rail. Has anyone got experiance with 'potting' rails onto a frame? I'll explain a bit more. I'm thinking ok, so I get some warpage when I do my welding, I go back and grind the mounting faces for the rails and get them to a fairly close tolerance. [ lets say 1/32" max deviation -peak to low spot- for really rough-not very well ground surfaces.] Would it be possible to use an metal filler epoxy[or JB weld, or something of this type of filler/epoxy] to help install the rail. If I was to put the epoxy on the bottom of the rail, then place it where it's going [ the mounting holes are all there and d&t'd] and then use a machinist's level and the screws to tighten and true the rail at the same time. Starting at one end, just tighten down at the high spots to bring them level with the lower spots. The lower spots will have a bed of epoxy under them, while the high spots will most likely have very little epoxy under them. Just leave it until things harden up and you've got a perfectly flat rail. A person could also put some type of release on the bottom of the rail so the epoxy isn't perminatly bonded to it and it's still removable.

Any "got-ya's" on going this route?

Jerry

[High Seas]

Jerry - - FlyGuy
Sorry, I'll back up a moment... and hopefully not replow some ground already worked. Regarding your rack and pinion set ups. I was browsing our members web sites and came across this one:
http://www.nexengroup.com/nexen/jsp/.../news?id=@7995
Looks VERY INTERESTING - sort of a pinion-roller bearing on a rack? Haven't followed up with any pricing, etc - but there ya go...
Jim

[jimbo]

Look at http://cnczone.com/forums/showthread.php?t=11024, it is the only diy router that I know using the metalized epoxy for joints and rails. He has a pretty good write up on his site.

[JerryFlyGuy]

Looks VERY INTERESTING - sort of a pinion-roller bearing on a rack? Haven't followed up with any pricing, etc - but there ya go...

No worries about re-plowed ground Jim, I'm always open to new idea's and even re-thinking old desicion's from different angles.

I've actually seen these before and they do look very promising, there are only two issue's I see w/ them.

They seem to better fit the smaller size unit's due to their restrictive force limitations. The smallest unit is only rated for 225lb's force... which is about 1/2 of the force delivered from 1 of my steppers. So I'd need to jump up several level's to a higher [ bigger] setup, the issue then become's stepper resolution. 1 rotation of the larger RPS25 pinion's gives 9.8" of travel. This would require me to re-gear down a fair bit [ I'm currently using a 1.0"PD gear], and in doing so.. I'd radically ramp up the torque even more, sorta a catch 22 issue.
These rack/pinion setups are kinda tricky that way, either you get it to work the first time.. or you have to tweak and play w/ it to get a reasonable setup. I found this issue even with the steel gear's I'm going to use. It took me a while to get what I wanted, and even then it ment not using the stepper I wanted simply because it was too big.. I was over the load rating of all the gears by as much as 2 times.. [I have a post elsewhere on here that ask's about this.. here ]

Keep your eye's open though.. I'm always looking for new idea's
and thanks for offering this one! There's lots out there that I've never seen I'm sure

Jerry

[JerryFlyGuy]

it is the only diy router that I know using the metalized epoxy for joints and rails. He has a pretty good write up on his site.

Thanks Jimbo, I'd seen this a few months ago and lost the link.. It's where I'd got the idea from.. but forgot exactly how he did it[ I was planning a different way.. however I think his is better... get it set then inject the epoxy]. Anyone else done this? Is that Moglice easy to work w/ could a guy inject it as this other fellow did or would it be to thick??

Jerry

[abomb55076]

May I ask where you managed to obtain all of those parts for soo cheap?

[JerryFlyGuy]

May I ask where you managed to obtain all of those parts for soo cheap?

Sorry there Abomb.. what parts are you talking about..??

Jerry

[Geof]

I suspect a difficulty you might run into trying to bed things in epoxy is having enough time. You need to be able to confirm the alignment of your rail and adjust it before the epoxy sets. I think if you expect to be able to start at one end and work along, or in the middle and work both ways, without having to go back and forth tweaking things you are being very optimistic. Also if you find some spots that have gone too low there is no way to push them back up. They might spring up if you release the bolt but then you have a cavity in the epoxy.

[JerryFlyGuy]

I suspect a difficulty you might run into trying to bed things in epoxy is having enough time. <snip>

Geoff, your VERY right.. and after posting that, I got that link that Jimbo posted and re-read what he had to say. This brought to light a product called Moglice [Moglice.com] in there they explain how to do it all and make it work. The trick is to actually mount a place the rail in its needed position.. get it level, parrallel and plumb w/ the other rails and then put a dam around it and inject the epoxy [ or whatever the heck moglice is... I suspect its epoxy] after 18 hr's of cure you've got a perfectly aligned and flat set of rails.. that is.. if they started that way before the epoxy injection. I think also in area's where the rails are sagging a person could probably pull them up w/ some wood blocks that mate w/ the rail and set screws to adjust them.. It just might work Jim dandy.. Ah well... I've got a week to stew on all this.. I'll be out of the office and thats where I do my best thinking... when I'm supposed to be thinking about other stuff..

Adios Amigo's [ and Amiga's???]

Jerry

[jimbo]

Another link I have seen posted here before is http://www.lmwatts.com/straightedge.html

[abomb55076]

I was woundering where you got all of those linear slides for soo cheap....

[jimbo]

abomb, I guess you are referring to me. I got the rails at a local surplus store. Bought the rails one day, then the blocks 1 week later which were found in a different part of the store, that is why I got them cheap.

[JerryFlyGuy]

Ahhh.. well finally got back home and now am getting back onto the Mill designing again. Travelings fun.. but not as much as this

Another link I have seen posted here before is http://www.lmwatts.com/straightedge.html

Yup Jimbo, it would appear that you an' me are looking at the same stuff
on the net. I've also come across this site and at first thought I'd go this route to get a flat enough member to mount my rails on. After reading what Moglice has to offer and what they propose, I'm thinking this route won't be nesc. Or... at least not to the extent that I'd originally thought. I'd tend to think that the amount of time required to get the structure flat enough would be exponentially porportional to the final finish. If you only want to get it to w/in 1/16" then you might be able to do all 20' of one member [ in my case] in 2-3 hrs. If you want to get it down to less than 0.005" then it may take.. weeks..years? I dunno.. but MUCH MUCH longer... I think I might be able to get my structure close enough just simply by taking my time w/ welding and then heat shrinking where it needs it.. I'd think if I had to put a max of 1/16" of moglice all the way under each rail... that this would be totally acceptable. As far as I can tell it shrinks very little and is very strong and stable.. [well I read the whole PDF of it but I won't go into all the details ] I plan to use a water level [ tube filled w/ water and alcohol to kill the surface tension] to level things over the 20'. I'll just simply set on corner of the x axis as my datum and level each side member to it so that each END is level w/ the datum. This will be accomplished after the side members have been straightened [ground or heat shrunk flat to +/- 1/32"] Then build jiging blocks to position the rail [ they'll be loc'd every 12" or so along the rail]. Get the two x rails flat and parrallel w/ each other via machinist level and then pump in the moglice. Do the same for the Y axis.

Anyone used Moglice or its equiv?? What did you use for the dam's? I've read "oil based clay" [or maybe it was puddy] what the heck is oil based clay/puddy???

Jerry

[Geof]

I am dubious about your epoxy gap filling idea. You will have to spend a lot of time aligning the rails and holding them in position, if you inject the epoxy under too much pressure you will move the rail, if you use too little pressure you will have voids, when it gets hot the epoxy is going to try to expans more than the metal so it will deform out of the gap, when it cools down again the epoxy will simply shrink and leave voids, if your main structure gradually relaxes all the built in stresses over a period of time your rails go out of true and you have no way to rectify this without starting from scratch.

So I have a suggestion shown in the picture. The rails are bolted to a subplate and this assembly is trued and levelled with adjustable bolt assemblies. Short 9/16"-18 bolts are drilled through, the head faced and these are threaded into the subplate from the bottom. Long bolts 5/16"-18 pass through the subplate, through the holes in the 9/16" bolts and into holes tapped in the main structure. The 9/16" bolts give adjustment and the 5/16" clamping.

There would not be much more work building this permanent adjustable mounting method than there would be in doing your alignment for the epoxy bedding and you would have the option in the future of correcting for main structure warpage.

[JerryFlyGuy]

Geof, you bring to light so good suggestions. Attached is the plan for installing the moglice. If memory serves my correctly, the epoxy they use has a very similar coef. of thermal exp to steel. I think I could get the rail into position to keep things from moving around. On their website they talk about how to inject the moglice to ensure that you have no voids and little pressure. I would suspect that they wouldn't put all the info on their site that they do, unless it worked as advertised, they have a fairly decent following so I suspect it does. The mat'l I plan to use "has the viscosity of motor oil" so it shouldn't be to hard to inject. Being as its going to be injected into a fairly thin area, I don't expect to much in the way of exothermic heating. I've [ while building our fiberglass airplane] seen a small cup of epoxy go "off" and it got so hot I couldn't hold it anymore.. however this was in a cup which has a way larger thermal capacity than a spread out thin layer 1/16" thick. They also show how to move along a rail [ or whatever] and inject in stages to keep the pressures to a minimum and yet have no voids. They do this by leaving vent's in the puddy dam along the part [ assuming a long skiny thing like a rail] you pump in the first vent until the stuff starts to come out the next vent 12" [or so] up the rail, then plug this vent and move to the one where it started to ooze out... insert your tip [ they supply you w/ empty caulking tubes that you fill] and keep injecting until the next vent starts oozing. ETC

I think building a plate into there and adjusting it via bolts is going to be alot more work simply because to properly support the rail you'd have to do this at least every 6" if not less. If in the future the structure does move I will have some control still because of the way I'm tieing it to the floor. I won't be able to put lots of correction into the structure, yet it shouldn't move that far in time. Also if it did shift somehow more than I can correct via my mounting, then I could re-jig the rails and add more moglice to get them back level. I think there's still lots of options.

I dunno.. I think I'm gonna try it at least for now I'll be sure to let you guys know how it works.. this is a little while down the road right now anyway.. I don't even have the rails I need yet!!

Jerry

[beone]

Guys, NASA has a special term for what you are doing, it is called "conformal Shimming". Its on everything they launch.
Dave

[JerryFlyGuy]

NASA ......what you are doing........."conformal Shimming"..... everything they launch.

It's great to know that your doing something that the big guys do.

I never thought the day would come when someone would say, 'oh ya.. thats what NASA does.. on EVERY rocket the launch' about something I'M trying to do...

Thanks Dave

Jerry

[JerryFlyGuy]

Well I looked into the cost of using the moglice [DWH 310FL] for my rails. It turns out that its pretty pricy. Its still affordable but it got me to looking. Devcon [devcon.com] as what they call a Plastic Steel -- Liquid 'B' I can get it for less than half the price of the moglice. I don't know for sure that they fill the same amount lb for lb but I'm expecting it to be close. Anyone ever used the Devcon stuff for this type of work?

Opinions welcome!!

Jerry

[WhiteTiger]

My experience with the devcon has been less than fun. Been a long time since I used it since it was pretty miserable, so maybe it's been improved since then, but the stuff used to go brittle hard in a few weeks and split out under even light loads.

If you want something with huge adhesion, physical stability, and resistance to most oils and solvents, go to www.brownells.com and pick up some acraglass bedding compound. It too is a bit spendy, but it goes a long way and has good strength (it's used to bed magnum rifle actions and stands up under the heavy recoil).



Tiger

[JerryFlyGuy]

My experience with the devcon has been less than fun.
<snip> the stuff used to go brittle hard in a few weeks and split out under even light loads.

If you want something with huge adhesion, physical stability, and resistance to most oils and solvents, go to www.brownells.com and pick up some acraglass bedding compound.

Tiger, thanks for taking the time to put this on here. I went and looked at the stuff you mentioned and it does look like it would do the job but looks REALLY spendy. I figured out that I'd need 3Kg [ 6.6lb's] of Moglice , if I was to do that via those little tubes, I might be buying a fair bit!! I'm glad you mentioned about the brittleness of Devcon. Thats really what I needed to find out. I think that Moglice is really the 'stuff' and like the saying goes, 'often imitated but never duplicated!' If you want something to do the job, you just have to buy the real stuff. I phoned the supplier of it and got a price of about $600 for what I need [ including about 25% extra for those 'unknown' issues that might arrise while using it] I guess when you compare how much the price of the rails and what not are, this is one of the cheaper things to buy, but boy is the material costs adding up FAST Now... if I can just convince my wife that my machine must go in the garage, instead of her bug....

Jerry