[austin.mn]

I already have a 6' X 10' table, however, it is too big for my tiny workshop... So, I have decided to try selling it and build a new machine. This time, going for a more modest 5' X 4' gantry. On my current table I am using Mesa electronics boards for the THC and I will again use that same system for the new table and EMC2.

The reason for the new machine... Well, I am using it more and more and it is not in my own shop, so if I have an order, I end up making the toolpaths here, then running across town, cutting a part for five minutes, then coming back to finish it all off. Plus, I think that my friend would like to have his garage back. I had planned to build a new shop here, but I just couldn't get it done this year.

I still have to buy the rack and pinion, motors and drives. Really all I have is the linear bearings and access to a steel shop with all the raw materials and big tools to use. I am planning to use some THK HSR 25's for the main gantry bearings, and V bearings for the other axis. The reason for those choices, is just because I have them. So, there is no point spending a bunch of money I don't have to. I was going to build it similar to just about all the tabletop routers you see, with the center drive under the table for the gantry. The linear bearings will be mounted upside down under the frame, which I hope will keep them clean. With my current table I have to clean my linear bearings all the time, I would like to stay away from having to do that with the new table.

The machine I am currently using will get listed on craigslist. It is well made, very heavy and has a water table and THC. I am going to keep the plasma torch and power supply. Which is an ESAB ESP-50 with a PT-37 torch. It has been working great, is 100% duty cycle and I just don't see any reason to replace it with anything else. So all someone needs is their own copy of Sheetcam and their own plasma torch and they would be up and running. Otherwise, I will have to cover it with tarps and park it outside until I get my big shop built... who knows when that will ever happen.

The plan is to get this thing built and operational within the next month. The sooner the better, I really want it to be functioning and bugs worked out before I get too busy with it this winter.

Next on the agenda is to run over to a friends shop to use Solidworks and get the plans all drawn up.. I hope I can remember how to use that software efficiently... I will post some screen shots when I get them done. Should be this weekend.

[austin.mn]

X and Y motors and drives have been ordered. I should have them next week. I am going to wait until they arrive before I order up the rack and pinions. I want to confirm the output shaft size. They are an 8:1 gear reduced Nema 34 stepper, I am expecting them to be pretty smooth. I still need to look for another drive for the Z. I have a few laying around, but I would like to try and keep all the drives the same if I can. It will make the wiring look a little more uniform.

that's all for now.

[gurew]

this thread needs pictures

[gurew]

also if you have the gear reduction already. there is no need to go with the nema34...however if you already have the nema 34, you def dont need the gear reduction and can save some money there...

[austin.mn]

Well, I have made some changes since my original design ideas. Once I got the new motors with the gear reduction on them and hooked them up, I realized they were unstoppable. :wee: So, I was pretty pumped about that. Then I started to go through my design criteria and saw that I wasn't certain that I was going to be completely satisfied with having the gantry tied together under that table and running on only one motor. So, I have decided to order up another motor and gear reduction. Sure, it will add to the cost a bit, extra motor, drive and rack and pinion, but I will have the satisfaction of knowing I won't have any racking issues. Then a friend let me know that he had some THK HSR45 rails laying around, and I found some bearing blocks for them on Ebay, so I have expanded the cuttable area of the table slighty. Still keeping single car garage friendly. My 6X10 isn't all that friendly, the overall size is about 7'X13', the new table will be 5.5'X6' and I have a nice spot picked out for it already. The rails are a bit overkill, and I think the motors are too.. but I figured, why not go balls out on this one. I already busted the original budget... which was, use what I had laying around and buy only what I had to...

I still have to order up the rack and pinions, 3 sets... the two for the lower drive will be fusion welded to the half inch thick plate that the lower linear bearings are mounted to. I will be bolting the upper rack to the top of the gantry. The motors will all be mounted on a pivot (still yet to be drawn up) and will have an air cylinder with regulated air pressure being the force that pushed them up against the rack. There will be a lever on the front of the table which will allow me to disengage the pinions from the rack and I will be able to just push the gantry out of the way. I can't even tell you how many times I have pulled steel out of the truck and went to through it on the table and couldn't because the gantry was in the way... ok, its only been a few, but if I can move the gantry without firing up the computer that is still a bonus. Plus having it be a manual air valve will allow me to ease the pinion into the rack without slamming the teeth together. Almost the entire frame will be made from 2"X5" .1875 tubing. I haven't looked to see how heavy the model is yet, but I am pretty sure its not going to be light.

Feel free to chime in with any concerns or comments.

[gurew]

might want to check and make sure your linear slides can support the weight of your gantry and everything attached to the gantry mounted like that....

[austin.mn]

Those linear rails are huge! I looked up the static load rating and if I remember correctly it was around 30000 lbs. I think that it will be fine to hang 150# of gantry from them like that. As far as the other loads go, I should be able to accelerate the gantry at over 6G's and the bearings will still be fine. They are extreme overkill.

[gurew]

its not about what its rated for static loading...its about if they can support weight upside down

[austin.mn]

I understand what your saying, I wasn't able to fine a reference to mounting preferences for the linear rails, but, I am pretty sure I will be just fine there.

[gurew]

you cant mount it like that..thats what im saying..they are only meant to be mounted horizontally or vertically with gravity being on the face of the rail...not backwards...if thats the way you want to do it then you will need a round linear rail but then it wouldnt be supported


unless you made a bar run a few inches lower from that top frame rail and mounted your rail to that facing up...if that makes sense...

i know 100% for a fact you cant mount a linear rail that way

[austin.mn]

I think that the reason I couldn't find a mounting preference for these rails is that it doesn't matter which way you mount them. Here is an excerpt from the THK site:
"Parallel to THK’s HSR series, the four-row design enables steel balls to have four 90-degree angular contacts between the block groove and the rail, so that forces coming from any direction will counteract equally, leading to equivalent loading.
This arrangement can be applied on any kind of machines that compared with Gothic counterpart, the X type four-row design possesses self alignment, high rigidity, high accuracy and longer lifetime. Even if significant deviation exists either on the machine itself or due to the installation, it can be rectified spontaneously coming with swift and precise linear motion."

So, I am not at all worried about mounting them upside down. I do understand what you were saying and I do know that some bearing types are fairly unforgiving on deviating from the manufactures recommendations, but with these I do not expect there to be any issues with these particular bearings.

[gurew]

by all means do what you want but there is a reason they dont talk about mounting like that....because 1) no one mounts ilke that 2) its not built for that type of load. i would call THK if i were you...better yet skip THK all together and check out igus® - Plastic Bushings, Linear Guides, Cable Carriers, Continuous-Flex Cables and give them a call...they can help you in under 5 min and tell you what load it can support....

[austin.mn]

I don't have any concerns about mounting them upside down. If I was using a small linear bearing and was planning to have a load that was any where near its rating, that would be one thing, but I am putting a 150 pound load on a bearing that is rated for 30,000 pounds. I am pretty certain, there won't be an issue. To add to that, I am putting a plasma cutter on the gantry, so there won't even be additional loads from cutting on them.

[gurew]

thats like saying..im using torsion bearings as my wheel bearings..it will be ok....completely different load types

[austin.mn]

If you can provide any documentation that states that I should be concerned using an HSR45 rail in the manner in which I intend I would be happy to see it, but it really seems like you just like arguing? Which I don't see as helpful, and know one reading this thread will be able to find it helpful either.

[gurew]

good luck with your build as it wont work. call THK, im unsubscribing to this thread.

[austin.mn]

good luck with your build as it wont work. call THK, im unsubscribing to this thread.

So, you quite arguing, because you can't validate it at all, and your final statement is It won't work?

I am telling you, I would be happy to hear if I am heading down the wrong track with this build, but just saying "it won't work" and not having anything to back up your argument, is really counter productive. You really made me second guess myself, and I looked up even more information on the rails and bearings I intend to use. From what I can gather, that static load rating is from all four directions.

After checking on that, stuff I decided to do a little checking on your stats... and well it appears you haven't even built a working machine yet. I on the other hand have had the pleasure of building several. I have mounted rails in this manner before, and it worked just fine. That was even on a router, and using bearings that were much less robust than these. I have gone through school for mechanical drafting and robotics, I have been working on and with cnc equipment for almost 14 years now.

So, please, if you are going to add to the conversation, I am all ears and happy to listen. Just don't start an argument that has no valid reasoning behind it.

Now, does anyone else have a questions or comments about the design?

[I Lean]

Just one comment: It looks like mounting the rails upside down will protect them from dust 'n stuff, but if you moved them up to the side of the table it would allow you to make the sides of the gantry quite a bit shorter. Shorter=lighter, and a lighter gantry = faster acceleration/deceleration, which is awesome for plasma.

[austin.mn]

I had thought of that but....

I am going to Fuse the rack to a .5 X 4" CRS then bolt the linear bearings to that. That keeps the rack and pinion shielded from the dirt and crap, which will allow me to lubricate it. I have also considered making the gantry with aluminum, but the ease of welding steel, for me at least, makes building it the way I am a little easier.

If you look at the drawings, the base will be welded (I still have gussets and more framework to add to the base) The cross beams will be bolted to the base, that way any warping from welding will be able too be shimmed out. The CRS and linear bearing rails will bolt onto those cross beams, and again, I will be able to shim them if needed. I may take a second look at the construction of MadVacs router, he used Moglice as the shim material.

There will be two 1200 oz/in Nema 23 steppers driving the gantry, through an 8:1 gear reduction to 2.25 pitch diameter pinion. That should allow for some pretty rapid acceleration. My current machine runs off of one Nema 34 640 oz/in motor and it does pretty decent on acceleration. In fact one of the big changes that will make the largest difference from that machine to this one is that I will be tightening the pinion to the rack using an air cylinder. My current machine has the tendency of jumping away from the rack under hard acceleration.

Another big thing that will make this machine accelerate pretty good, is the Mesa 5i20 card and EMC as the controller. I went from barely being reliable at 500ipm running out the parallel port to being able to rapid at over 1800ipm using the mesa control card. It really helps to have a clean signal going to the motor drives. I never even did try to make it go faster than 1800ipm either, I am pretty sure it would have kept on increasing in speed. After running it that way for a week, I slowed it down to 1200 as it was just too fast for me to be comfortable with it.

One more thing that I intend to do is make a magnetic break away for the torch. Then I will feel better about running faster rapids without hurting the torch on a tip up.

Well, I better get back to getting the details added to the drawing tonight. I still have to add a water tank, motors, frame gussets and cable tracks an entire Z axis....

[Dustin407]

Austin,

Good Luck on your build. I think your overall design is very nice and should work just fine. As for the rails being mounted upside down that will work just fine. The balls travel in a groove in the rail that locks them in so you can mount them any way you want.. The only input I have is stay away from the gas shock, I would go more mechanical and simple (spring). I think you will run into problems and headaches with the complexity and unreliablity of the air shock... Also Alum. gantry is nice, good for backlash ans quick turn around accel..

Gurew,

Im sorry but I think your input in these forums is worthless... Its like listening to my girlfriend for ideas on how to build a CNC machine. Maybe you should finish yours before you give others all these great ideas... Im sorry did I say ideas I meant arguing..