Not sure I'm ready for this - I've started building!

[ViperTX]

So, a technique that Thomson (darn I always forget...Thomsen) anyway.....what they recommend when mounting their round rails to the t-bar rail support...was a bed of metal epoxy to help the alignment...so you would only tighten the end bolts until the epoxy had set then you'd tighten the others. In your case you are setting the carriages on the surface plate and then placing your machined plate on top of the carriages...Is that correct?

[buscht]

Mike, it's always tough the first time. THK has good information about mounting rails and carriages in their catalogs and website. If you haven't done so, I highly recommend reading it.

I might have missed something in an earlier post. Do the individual carriages move smoothly on the rail? I do know that you can impart a twist or bow in the rail if it isn't mounted to a perfectly flat surface. The problem has to be in rail mounting, or the flatness of the rectangular tubing.

Are your bolt holes sufficiently oversize so you let the carriage align themselves? Tighten one carriage and leave the other just slightly loose. Move the assembly back and forth and check for smoothness. Then slowly tighten up the other carriage trying to see when it starts binding.

Another wild idea, get your THK distributor to come in and help you out. He might be willing to help out of the goodness of his heart, and the good publicity.

[Mike F]

Another wild idea, get your THK distributor to come in and help you out. He might be willing to help out of the goodness of his heart, and the good publicity.

That idea has certainly crossed my mind! All the other suggestions I have tried. I also have the THK General Catalogue with all the mounting information in and have followed it as closely as I can with the limited machining available to me.

My hair is getting thinner by the day but I will crack this one and that's a promise.

Thanks for your interest. This site is brilliant.

Mike

[Mike F]

Trent,

Sorry, missed one of your points - the individual blocks glide as beautifully as Torville & Dean (sorry showing my age and colours there )

Mike

[Mike F]

Finally got it sorted today. These things are so fussy. One of THK's boasts is that their systems of linear guides are quite forgiving of alignment discrepancies. Obviously not the kind of discrepancies I was able to build in

Well on the way to finishing the second carriage for the bottom rail after which I have to tie the two together with the gantry and probably find a new set of misalignments to sort out.

It is such a great feeling when something actually works after you begin to doubt your ability to do it.

Mike

[buscht]

Mike, after its all together and running, you wonder what the big deal was. Until then every little thing is a major hurdle.

Be prepared for more alignment issues once you go and try to attach the ball screw. I fought that for an entire weekend.
Trent

[arvidb]

Mike, what did you do to get it working?

Arvid

[Mike F]

Arvid,

Back in post #19 I attached a photo of the aluminium shims made to correct the out of plane rails. These were to be placed between the blocks and the mounting system. These shims were superglued to the box section steel shown in post #34 - that was the easy bit. Because the machined flats, on either end of the box section, were not in the same plane (dodgy, out of perpendicular milling machine), these had to somehow be corrected.

I used some peelable spray on adhesive to stick some 150 grit wet and dry paper to a surface plate then painstakingly rubbed the two shims down till they were perfectly level. This worked very well indeed though was time consuming.

Next, to make sure the top of the box section was flat this too was milled and a piece of aluminium screwed to it, against which the blocks are aligned. (see photo) You can just make out the aluminium strip at the top of the assembly. The blocks were clamped to this while they were bolted through the box section. Everything was now square and true - phew!

What I have learned from this is that when THK say their system of linear guides are tolerant of misalignment, they are not talking the same kind of figures that I am

Mike

[Mike F]

Well, progress at last, the clamps are off and the whole gantry is self supporting and moving freely - I've had a good day today after solving the problem of the square balls yesterday. The second block carrier went together first time and ran beautifully. I just had to get the gantry mounted that ties the two block carriers together. I was a little nervous as I was expecting the whole assembly to bind up and jam again but, to my surprise, it didn't. It ran almost perfectly, slightly stiffer than before but perfectly acceptable. The rails now need some slight adjustment to take out some very slight binding in one or two places.

Now I can press the laser line into action again to test for rail perpendicularity. I'll post some more pictures as I do it.

Trent, I've not yet worked out how I am going to mount the ballscrews but I am sure you are right about more alignment problems.

Mike

[Mike F]

A bit more progress.

The gantry was disassembled, cleaned up and lacquered prior to attaching the Y axis rails. This was done to stop the oil from the rails staining the MDF and the whole thing becoming grubby from handling. The lacquer used was a two part, acid curing cellulose that was sprayed on. Two coats were given, rubbing down after the first. This stuff is good as it goes hard very quickly and can be rubbed down with wet and dry paper (or very fine glass paper) after just half an hour, without the paper clogging.

Our small, Isel machine was again pressed into service to machine a drilling jig for the Y axis rail mounting. This was simply a piece of 6mm MDF that was accurately drilled with the appropriate spacing. The jig was clamped to the gantry side and the holes drilled through - perfect alignment

I had to work out how to attach the rails, as this time they would be fixed to MDF, not steel as for the X-axis. I figured it would not be wise to screw into the MDF so I drilled and tapped a piece of 700mm x 9mm x 5mm brass strip to take the 5mm bolts. You can see one of them in the photo below that shows one rail attached and the other not. This works well and spreads the mounting load much more evenly and there is no chance of it pulling through the MDF under operational loads.

The other photos show the gantry re-assembled and a close-up. I hope to get the Y-axis, Z carrying plate in place before we break for Christmas at the end of this week. Only two days to go!

Mike

[Mike F]

For some reason the photos did not appear with the previous post

[buscht]

Mike, great job! I can't thank you enough for sharing all this information.

I have had good luck screwing into MDF with something that we call a EURO screw. They are used in 32mm systems. You drill a 5mm hole in the MDF and these screws are designed for cabinet hinges and drawer slide mountings.

Also, threaded tee nuts work pretty well but aren't as pretty as your solution.

Thanks again
Trent