Preliminary Outline of my First Table

[lost_cause]

I'm gathering all the information and part specs to get ready to build a table. My initial plan was to find an inexpensive gantry package (the Precision Plasma 5x10 had been looking good), and combine that with a CandCNC electronics package with ubuntu/emc to run the show, and build the table myself. After a little looking around, I'm thinking of building a little more from scratch than I had originally planned.

I'll easily confess that fiero addiction's table build thread has been used for a lot of my plan, but as with every homemade and over the counter solution... there's always something I want different. I was a steel detailer for many years, so I've been thinking through all the connection points already, and have a lot of sketches scattered around the desk right now, and hopefully within a week I'll have most all of the fabrication details ironed out.

The one major detail I want to do that is different from most rectangular tables is to have the gantry span the long axis of the table. This idea has come about for several reasons: I initially planned on going with a 5'x10' table to utilize the largest sheet sizes I'm likely to work with, which would be 4'x8' or 5'x10', but shop space is always at a premium. After thinking about it, the odds of me ever cutting anything larger than 3'x5' are pretty darn slim, so what I'm thinking is to make a table that is between 5'to 6' long, against the wall, with a 3'to 4' dimension coming away from the wall, making it take up not much more space than a desk or table. By spanning the gantry over the long axis I can load the table with no worry of damaging the gantry or rails, as they will be parallel with the direction of the sheet load. Though probably not ideal, if I ever need to load a 4'x8' or 5'x10' sheet, I can pull the table out from the wall and slide the large sheet through and support the ends that hang over. I may even design in brackets for outrigger supports into the table at the start.

As far as the electronics goes... well, that's still up in the air. As with everything else, no matter how good or complete it is, thre's always going to be something I want to do differently, even if it's just something in the way the wiring and connections are done. I have a lot of years of experience working with computer hardware, so the physical assembly of the electronics package is not anything out of the ordinary, but specifications and functions of every part is a bit of a gray area - very light gray at that. The jury is still out on whether I'll do this myself or go with the over the counter package right now. Scavenging the PC components is just a trip to the basement and a little trial and error to figure out which of the parts I have stashed still work.

Following are some of my preliminary build specifications. For those of you in the know, please let me know if you see anything totally out of the ordinary. For the record, much of my steel size selection is based on what I have on hand - I probably have somewhere around 2 tons of new (though some 10yrs old) light angle, channel, flat bar and tube. I'll probably scan in some of the sketches I have going in the next few days.

Table: 6'x4'(+/-)Probably a finished bed that will support a 3'-6"x5'-2" sheet (1/3 of a 5'x10' sheet) Table Legs: 2"x2"x0.120", Table Side Rails: 3"x2"x0.120". Braces to be sized and located later.

Gantry: 4"x2"x0.120" spanning the long axis of the table with 2"x2"x0.120" vertical posts and 1/4" bearing and motor plates. #2 guide rollers and tracks (top and bottom) to support the torch assembly.

Torch Mount: Too early to determine. Will update when I catch up.

Electronics: Too early to determine. Will update when I catch up.

Software: EMC for running the table. I still need to find a solution for creating custom dxf files though. I've probably created 10k+ dxf files from steel detailing software packages, but I never learned any standard CAD packages. Anyone got any wallet friendly and gentle learning curve suggestions on CAD software? - Would prefer Windows based over Linux.

Thanks.

[lost_cause]

ok, i think i may have had a change of heart about the guide rail system i am going to use. i really like the neatness, simplicity, and low weight of the v-groove rollers and track used by fiero addiction, but after looking at the torchmate again, i'm thinking i may do something similar to that.

part of my problem is that i've looked at so many different ones, it's hard to make a choice. i like the approach of the cold rolled flat bar rails for a couple of reasons: it makes the hardware much easier to obtain. bearings are just standard ones now, instead of the machined v-groove ones, and the track is just a bar now. this should work great for the tracks on the two table rails, but i'm concerned about using this for the gantry.

i guess the issue boils down to how much weight you have in the gantry and still be able to drive it around with the motors? i'm thinking around the range of the 300 oz/in motors. i know that because it needs to be able to make sudden stops and changes in direction, the weight has to factor in. i am also going to take a page from the torchmate design and raise my table rails so that there is no added lever arm between the rails and the top of the gantry, but i assume weight still will be an issue.

for the table rails i was thinking a 3/8 or 1/2 by 3 to 3 1/2 flat bar laid horizontally. this should be no problem, but for the gantry, if i were to use the same flat, but turned vertical, and then reinforced with a 2x2x0.120 tube, the weight of a 6 foot gantry would be around 50 lb without the torch assembly (mount, rails, torch). is 50lb too much to toss around with these motors, or any motor for that matter?

[millman52]

i guess the issue boils down to how much weight you have in the gantry and still be able to drive it around with the motors?

for the table rails i was thinking a 3/8 or 1/2 by 3 to 3 1/2 flat bar laid horizontally. this should be no problem, but for the gantry, if i were to use the same flat, but turned vertical, and then reinforced with a 2x2x0.120 tube, the weight of a 6 foot gantry would be around 50 lb without the torch assembly (mount, rails, torch). is 50lb too much to toss around with these motors, or any motor for that matter?

Your stepper motors (4 assuming you salve a pair on the ends of the gantry) plus belt reduction pulleys & drive assemblys is going to add another 50+ lb. Then the gantry also has to carry the E chain & wiring.

I really think you'll need closer 700 oz in. motors to drive the entire gantry assembly to achieve good stopping ability + acceleration in the opposite direction

I have a 6' all steel gantry that bumps the scale upwards of 150#. To look at it you'd think NO Way! If you take the time to add up everything the gantry assembly has to haul around including fasteners, brackets, springs, wire, Yada Yada it all adds up pretty quick.

[lost_cause]

Your stepper motors (4 assuming you salve a pair on the ends of the gantry) plus belt reduction pulleys & drive assemblys is going to add another 50+ lb. Then the gantry also has to carry the E chain & wiring.

I really think you'll need closer 700 oz in. motors to drive the entire gantry assembly to achieve good stopping ability + acceleration in the opposite direction

yeah, my 50lb assessment of the gantry was only the weight of the 2x2 tube, 3x1/2 flat, and a couple of 1/4 plates on the ends. if 150lb isn't out of the question, i should be able to work things out. as i refine the designs, i'm sure i'll shave some weight in places anyways.

i'm still learning all of this, and the only table i've ever even seen (much less have any knowledge of) was probably in the 6 figure range, so i know nothing about setting up and sizing parts for a small table. you mentioned belt reduction - i've seen a lot of posts saying that it isn't needed for a plasma only setup. what's the theory behind determining when they are needed? does if have to do with the weight issue and the oversized motors it will take to toss my heavy gantry around? hit me with some background info to digest

final question (for this post) - i'm assuming it would be best to design this starting from the top and working down, so you can correctly size each supporting piece of hardware as you go. that being said, i need to figure out what to use for the z-axis. i'm assuming one of the pre-made slide bearing assemblies is the way to go? any suggestions on what to look at first for the torch mount and vertical motion?

if it matters, my torch will most likely be a thermal dynamics cutmaster 52 or hypertherm 45. ideally i will go with a machine torch, but depending on how spendy i feel at the time of completion, that may change. i'd like to have both so i can leave the machine torch in the table and just swap leads when i need to use it freehand.

thanks.

[millman52]

yeah, my 50lb assessment of the gantry was only the weight of the 2x2 tube, 3x1/2 flat, and a couple of 1/4 plates on the ends. if 150lb isn't out of the question, i should be able to work things out. as i refine the designs, i'm sure i'll shave some weight in places anyways.

i'm still learning all of this, and the only table i've ever even seen (much less have any knowledge of) was probably in the 6 figure range, so i know nothing about setting up and sizing parts for a small table. you mentioned belt reduction - i've seen a lot of posts saying that it isn't needed for a plasma only setup. what's the theory behind determining when they are needed? does if have to do with the weight issue and the oversized motors it will take to toss my heavy gantry around? hit me with some background info to digest

final question (for this post) - i'm assuming it would be best to design this starting from the top and working down, so you can correctly size each supporting piece of hardware as you go. that being said, i need to figure out what to use for the z-axis. i'm assuming one of the pre-made slide bearing assemblies is the way to go? any suggestions on what to look at first for the torch mount and vertical motion?

if it matters, my torch will most likely be a thermal dynamics cutmaster 52 or hypertherm 45. ideally i will go with a machine torch, but depending on how spendy i feel at the time of completion, that may change. i'd like to have both so i can leave the machine torch in the table and just swap leads when i need to use it freehand.

thanks.

The actual weight your motors have to move is the entire weight of the rolling gantry ready to work + extra to overcome friction.

What you can get by with depends a lot on the material & amount of detail you want to cut. If you are going to be working with thin material & art type of work you need torque & fairly rapid stopping & acceleration. & to put is simply it needs to be like a sprint car. Torque for rapid stops & acceleration + speed to make dross free cuts on thin material.

Typical stepper motors develop pretty good torque but that drops off as speed increases. Then there is resolution (amount of detail in your work) Lets say you direct drive a 1" pinion. A 1" pinion is going to move it's axis 3.14" per rev. of the motor. Top speed of most steppers is 700-800 RPM. Direct driving is going to put your rapid speeds in the 2000 IPM range. Kind of like trying to pull a semi-trailer with a mini-van. Can't accelerate & just as important can't stop once rolling.

Once you determine the actual weight of the gantry you can calculate the motor size/gear reduction combination needed to move & stop the gantry at desired speeds. The catch to pre building is NEMA 23 frame motors are limited to around 500 oz in torque. Much beyond 500 oz. in. you'll need a NEMA 34 frame size.

If you are going to incorporate a pre made Z axis & plan at some point to use a THC you need to be sure the lead screw in the Z axis will work with the requirements of the THC. There you need to speak with one of the THC suppliers.

I bought a HT machine with hand torch attached & bought a machine torch to match. Don't know about TD but HT torches are a quick attach at the machine.

[lost_cause]

ok, i'm sort of waffling on my design a little. at first i was going to go with the v-groove rollers, but then i decided that i wanted to go with standard flat bar for rails. after looking at this plan, while cheaper, i decided that it involved a lot more guide bearings to keep things lined up, so i'm back to the initial plan of using the v-groove guide rollers (for now).

i've put a little of the design down on paper and i've posted it here. as you can see, i stole a page from fiero addiction's table design, but i've also gone with torchmate's elevated table rails to eliminate any extra height to the gantry. in theory, this should help acceleration and deceleration by removing that eccentricity. i'm also planning on building a belt reduction into my table form the start, if it turns out that i don't need it, i can just change it to a 1:1 ratio.

i'm going to work on a plan for the z axis next. if anyone has any comments about my design that may need attention, please let me know.

thanks

[lost_cause]

i almost forgot... i can't quite wrap my head around the belt drive issue. i first thought it was just a large circular belt that turns. the more i look at how everyone's table is set up, it looks like the belts are stationary, and the rest of the drive train rides on the belts, sort of like a rack and pinion system. is this the case? is the belt just one strip of belting and not a continuous circular belt? if so, what is the best method of anchoring the ends?

[millman52]

i almost forgot... i can't quite wrap my head around the belt drive issue. i first thought it was just a large circular belt that turns. the more i look at how everyone's table is set up, it looks like the belts are stationary, and the rest of the drive train rides on the belts, sort of like a rack and pinion system. is this the case? is the belt just one strip of belting and not a continuous circular belt? if so, what is the best method of anchoring the ends?

Usually McMasterCarr & others that sell continuous belt has end anchors for mounting the ends.

The only thing I see in your drawings. The dual V rail across the gantry may be easier to keep accurate if you mount the V rail to a length of cold rolled flat. say 3/16" X 3". The rounded corners of the steel box tube may give you problems. Or even better use a piece of aluminum box tube that has square corners for the gantry rail.

Have you priced a length of 20MM profiled linear rail & bearing(s) & compaired that to the price of dual V & bearings & rails? The profiled linear will be much easier to get lined up & the preload of the bearing will remain constant over the entire length.

[lost_cause]

Have you priced a length of 20MM profiled linear rail & bearing(s) & compaired that to the price of dual V & bearings & rails? The profiled linear will be much easier to get lined up & the preload of the bearing will remain constant over the entire length.

i wish i knew more than i do about this stuff... maybe by the time i build my second or third cnc machine i'll know what all the available components are. i searched for profiled linear rail and came up with two different types: the round rail and some rectangular rail and bearing blocks, but both seemed to be around the same price range.

i'm sure there are cheaper places that i didn't find, but for 6' sections, both types of profiled rail seemed to be around $150 for rail and blocks. assuming i would need two for the gantry alone, that's around $300 to plumb up the gantry. i can buy 2 6' sections of v-rail, 4 v-rollers, and 2 concentric and 2 eccentric bushings all for about $135 plus some shipping. unless there's some better deals out there, it's nearly double.

aside from the cost, another goal of mine is to use as few specialized parts as possible. i'm sure i'll never need to, but if something ever fails and needs replacing, i figure that the v-groove parts seem to be pretty common and standardized. i don't know enough about the profiled rail to know whether i would be able to buy one part to match a few years down the road, or whether i'd have to re-engineer a lot of stuff.

and thanks for all the help so far millman52, i'm going to have a million questions before this is all done.

[millman52]

i wish i knew more than i do about this stuff... maybe by the time i build my second or third cnc machine i'll know what all the available components are. i searched for profiled linear rail and came up with two different types: the round rail and some rectangular rail and bearing blocks, but both seemed to be around the same price range.

i'm sure there are cheaper places that i didn't find, but for 6' sections, both types of profiled rail seemed to be around $150 for rail and blocks. assuming i would need two for the gantry alone, that's around $300 to plumb up the gantry. i can buy 2 6' sections of v-rail, 4 v-rollers, and 2 concentric and 2 eccentric bushings all for about $135 plus some shipping. unless there's some better deals out there, it's nearly double.

aside from the cost, another goal of mine is to use as few specialized parts as possible. i'm sure i'll never need to, but if something ever fails and needs replacing, i figure that the v-groove parts seem to be pretty common and standardized. i don't know enough about the profiled rail to know whether i would be able to buy one part to match a few years down the road, or whether i'd have to re-engineer a lot of stuff.

and thanks for all the help so far millman52, i'm going to have a million questions before this is all done.

Lots of people on here are using HIWIN linear rail & bearing(s). Pretty sure one of the companies that have it reasonably priced is http://www.automation4less.com/linear.htm

For plasma/ox-fuel (1) single 20 or 25 MM profiled (rectangular) rail is all you should need. If your Z axis is fairly light (1) bearing cartridge will be fine (2) at most.

Look at picture below for an idea of what I am talking about. The rail shown isn't HIWIN but that doesn't matter.

For $15 more money you will save several hours of time when it comes to aligning 2 V rails to make 1 single axis.

There isn't anything wrong with using V rails I think it's a good system for plasma machines. & Is the way I'd go on the side rail. Mounting them in a pair to make a "captive" linear rail will take time to align to the point it's preloaded in 1 spot & has play a foot down the gantry.

[lost_cause]

the more i look, the more i find something i like better. i think i'm going to watch ebay for the next week or so and try to pick up a few used linear rail setups. i have been thinking and if i go with those rails i will probably use them on all 4 driven axes. i know most think it's best to only use them on one side of the gantry, but i think lining up two of those rails should be pretty simple. since the entire gantry is going to be made of steel, expansion from temperature should be consistent. i think that using them on both sides of the gantry will make things easier to line up and level.