[jhuddleston]

First let me say I am astoundey by the raw and refined talent that this forum displays. I am in awe with jcar and his plasma table.

I am looking to build a plasma with a cutting envelope of roughly 5 x 8. I know when I startasking questions everybody is going to have an opinion and I appretiate any and all feed back. The table I am going to build will see heavy daily use and will cut metal up to 1".
1. Should I use slides with a rack and pinion set up or should I use ball screws and slides.
2. My largest fear is building a table and having racking issues on the x.
3.I have no problem with the fabrication, due to the simple fact I own a machine and fab shop. I have a good solid background in electronics. My issues are with design. Where can I find some basics on design for mounting servos, steppers , pinions, ball screws ect..

I appretiate will any and all help.

[millman52]

You most likely will want to go with rack & pinion. Probably end up with to much whip in lead screws over that length of table.

You shouldn't have "racking issues" if you mean gantry twisting if you ether use a single drive motor with a jack shaft or 2 motors slaved together & R&P down both sides of the table.

I have just finished & put to work a 5' X 10' with steppers slaved together on the X axis works well.

[jhuddleston]

I am looking to purchase my linear slides and need some input on the best lide configuration for my x and y. I would also like input on where to purchase them.

[millman52]

linear rail is avalible several different places

Do a search for Hiwin they have a banner ad on this site that pops up every now & then.

I think Keling inc also carries linear slides & bearings.

Just check on their individual prices & availibility.

There are many manufacturers jusc check around

[jhuddleston]

Ok I am confused as HE##

I called HiWin they are going to give me some options on rails based on my info and Keling inc had no clue how much weight their 25mm rails supported. I am shooting for a work envelope of 96 x 60 Does anyone have any suggestions on what brand and type of rail to use. I figure my gantry to be between 150 and 200 lbs. I am not sure if I should use a single block on the linear rail or doubl. I am also wondering if I shoud use a y axis linear slide with a ball screw in it or opt for a pinion on the y axis

[jhuddleston]

Ok I am confused I called Hiwin and they are going to give me some suggestions on rails based on my information. Keling inc has no clues on the amount of weight their 25mm rails support. I am looking to have a cutting envelope of 96x60. Do I need double blocks or singled on my x axis and can someone give me some insight on what type and brand of rail I should use for my x. I am thinking of going with a linear rail and ballscrew through the center for my y and z. Does anyone see a problem with that?

[millman52]

If you are using linear rail along both sides of your 96" or X axis I think you'd need 4 bearing trucks.

Ball screw will probably work ok on the Y as long as it's large enough in dia. & or course enough pitch to keep the speed (RPM) low enough to prevent whip in the screw. Keep in mind with the Y all the way to one side you'll still have 5' or a bit better of unsupported ball screw shaft.

[jhuddleston]

http://www.hiwin.com/ls/kk.html


This is what I am looking @ for the y axis and a shorter one for the z

[scrambled]

I purchased my linear rails from Rick at Superior Bearing. http://www.superiorbearing.com/ .

I had great service from them. With zero complaints.



Steve

[zeoncomp]

I purchased my linear rails from Rick at Superior Bearing. http://www.superiorbearing.com/ .

I had great service from them. With zero complaints.



Steve

I've been dealing with Rick also and I have nothing but PROPS for him. Outstanding service and honest.

Rack and pinion is the way to go - make sure you go for the 20degrees angle. You'll find great deal of informations in this forum if you do the right search.
For the electronics I'm using one of the packages from CandCNC.com
Tom (Torchead - in this forum) is very knowleadgable and helpful. The install is not complicated and works flowless. Call him and he'll tell you all about it. Great service there also. One thing to remember is that for that size table you'll need 2 X (or Y) axis - the long axis. Otherwise you'll have too much balance in one side for sudden moves. So you should be looking for a 4 axis package. You can look at the pics of my table http://picasaweb.google.com/true4x4/PlasmaTable
Maybe you'll get some ideeas - I am in process of adding the second X axis as we speak.
Good luck

/Remy - Colorado

[jhuddleston]

Does anyone know where I can find some 100" racks or am I goint to have to put 2 or 3 together? I found some 6ft rack @ McMaster CarrOnce I lock down racks and linear railsI will start building the table. I hope to finish it quick form. I have the ability to work on it continously untill it is finished.

[Jcar]

jhuddleston,

I'd go with rack and pinion, it's more resistant to dust and is a better choice on longer machines (ie...no ballscrew whip as millman52 stated earlier).

If you're concerned about the rails not being able to handle the load, do a little surfing and find the manufacturer's data sheet for the rails you're considering. The data sheet will have load ratings for different orientations.

I think you'll find that two 20 series (20mm) rails will be more than enough to support your gantry. Use two trucks per rail, and span them a foot or so apart. It's just good engineering with rails of this size.

You've probably noticed that some of us are using one rail and truck for the axis that spans the width of the gantry. We're getting away with doing this because we're using 35 series rails or greater. These things are huge. The trucks alone weigh 5-7 pounds and are 5" square and 2-1/2" thick. They have load ratings in excess of 6000 lbs. The only problem with these larger rails is the cost. If you're buying new, I think it's more cost effective to go with two 20mm rails. One word describes why I used one....... ebay.

Make sure the trucks come with wipers. Most do, however I've seen a few where wipers are optional.

As stated in an earlier post, I'd highly recommend that you drive your gantry from both sides, either with dual drives or a single drive and jack shaft. Doing so will eliminate any racking issues that you may be concerned with.

Good luck with your build, and keep us updated with your progress. Even though many of us have built and are running our own machines, we still enjoy seeing a new machine come together. It's kind of like CNC machine builders porn.

Jcar,

[millman52]

Does anyone know where I can find some 100" racks or am I goint to have to put 2 or 3 together? I found some 6ft rack @ McMaster CarrOnce I lock down racks and linear railsI will start building the table. I hope to finish it quick form. I have the ability to work on it continously untill it is finished.

Racks are easy to join & don't need any welding on the joints. here is an example from my build of how to maintain spacing of the teeth through a joint. http://www.cnczone.com/forums/showth...t=31133&page=4 post # 40. Just be sure your splice is made with the joint being in the gullet or bottom between the teeth .

I am using a single run of 15 MM rail on my Y axis with 2 bearing trucks. Just what I could find on Ebay at the time. It seems to work just fine. However the side of me that likes things "heavy duty" don't like the looks of it. There Is no detectable play in the assembly. I guess time alone will tell me how well it holds up.

Another thing that make ball screws NOT the best choice for drives on a plasma table is: How the HE** do you plan to keep the grit out of them & oil in.

I used a screw on my Z but I have it housed up inside a telescoping tube with a dual "O" ring as a wiper seal on the telescoping end. I went with this arrangement to keep weight & bulk down as opposed to having to build a belt reduction & all else that would become bulky & heavy just to obtain 6" of Z travel. I also wanted pretty high resolution on the Z because it would take "baby steps" when jogging up & down manually on the oxy side.

You will need fairly high resolution if you are going to use a torch height controller for plasma such as a THC1000. If not the THC controller will overshoot & continually search for it's desired height.

Again Tom (Torchhead) at CandCNC.com can advise you here.

[zeoncomp]

jhuddleston,

..... It's kind of like CNC machine builders porn.

Jcar,

Stop .... Stop .....

[jhuddleston]

I just want to thankeveryone for all the help and keep everyone updated. I just sent an email back to rick telling him to send me these rail. Obviously they will not ship untill next week.

MSA20S-2-SS-KK-FC+R2720-20/20-N = $292.15 each (X-axis, 2 req'd.)
MSA20S-2-SS-DD-FC+R1600-20/20-N = $206.97 each (Y-axis, 1 req'd.)

The jury is still out on my z axsis. anyone have anyinfo on telescoping tubes?

[jcc3inc]

jhud ,

A source of gear rack is:

www.stdsteel.com/gear.htm

Cost is about $23 ea/qty = 2; The rack in stock is 20 DP, 20 degree PA, lengths are 6 ft, rack cross section is 1/2 x 1/2". For matching 20 degree 20 DP pinions see Boston Gear or Martin Gear. To join sections, use a 4" long piece of rack overlapping the joint area meshing into the two pieces to be joined. I have a couple of dwgs I could email you with more info.

jccinc-at-owc-dot-net

Regards,
Jack C.

[harryn]

skip

[jhuddleston]

just wanted to let everyone know I am waiting on rails, trying to replace employees and recover from a vacation injury. I will be updating this post soon

[BIGCNC]

A good supplyer for gear rack is axisautomationinc.com they have them in 12'
lengths for $168.00 and $38 for the gears. 20 dgree pa and 24 pitch rack size is 1" face x 1.25 .005 culmlative error over 12' feet. The gears have .7500 keyed shafts. Good Luck With Your Machine.