Are JD2 and shop sabre type gantry overkill for plasma?

[mikeysp]

Hi. Planning a high quality build and I am trying to determine what makes a great plasma machine.

I have looked at the JD2 and Shop Sabre machines for inspiration and I am certainly impressed with the build quality; however, I ask myself if it is not overkill for a plasma only machine?

I have no intention of EVER making it a router.

Am I wrong in thinking a very LIGHT gantry, vs heavy duty? A torch and scribe are not all that heavy. Are they so heavy duty only to accommodate a router?

I am also thinking in terms of 8hrs a day usage.

Thanks. -Mike

[acourtjester]

You want a table that will not wiggle or flex when it moves, there is some weight being pushed around with cutting. No contact with plasma but there is some with scribe work. I prefer a fully welded table over a bolted together, and only fine threaded bolts when used for stronger grip.
Here are image of 2 of the table bases I built (black 4X4 unpainted 4X8)

[AlphaTekErik]

in my opinion, heavy bridge is best. more weight translates into less flex and vibration. the smoothest moving machines i see have a nice heavy bridge. granted i travel to several fab shops a week servicing cutting systems, i do not see much hobby level setups.

[mikeysp]

Tom, welded table makes sense, and is my plan. However, what about gantry style? The Shop Sabre and the JD2 have a serious beam with dual HiWin type linear rails several inches apart. Is that overkill for just plasma? I know they advertise using for router also. However, is their a benefit for plasma? Increased stiffness meaning noticeably tighter tolerances?

Thanks. -Mike

[mikeysp]

Eric, that is a very helpful observation. Do you have a favorite machine make/model or two that you would recommend as models worthy of copying?

-Miker

[weldguy]

Indeed a heavier gantry with well matched motion control will tend to be smoother and less prone to vibration but the same can also be accomplished on a significantly lighter gantry, for example PlasmaCam gantrys run very smooth and are very light and rudimentary in comparison. The advantage to a lighter gantry is that fast speeds can be achieved without throwing around a pile of unneeded weight which will require a very heavy and sturdy table and all of this costs more money. If you do not plan to use a router or do flame cutting a lighter gantry will server you very well, particularly if you intend to mainly cut thinner gauge metal for duct work fittings or artwork which can be cut at very fast speeds. A welded steel frame is something I would not go without so take all this into consideration along with your budget.

[mikeysp]

I will not do any flame cutting. I will have a scribe and utilize my Hypertherm 85 with a machine torch. I will be cutting both thin gauge on up to 3/4".

[SegoMan DeSigns]

Tom,

I'll split a "cute bunny" with you over the benefits of a welded table..

Welding warps things even if you have a good welding table to clamp it too, there are few mills big enough (at least in my area) to machine the surface flat again after it has warped. So now you no longer have a flat surface to work with.

My main frame was made out of 10" H beam and the cross members are a 4" I beam all bolted together, the makeup on the I beam would have required a 10* washer so I drilled and tapped it instead. An easy task with the right drill press and taping machine. I used stringers and X bracing to keep it square. The water tank and lower girders are reinforcing points as well (force multiplication applies here)

With 350 gal of water in the tank I'm a tad shy of 10K lbs this will support a 6'x12' sheet of 1 plate that adds another 2,800 lbs. I don't thik I would go any larger with a unitized design like this, I would have the gantry / rail supports separate from the water table w/ material support to prevent flexing under serious loads

OP

I went with a 4"x6"x.125 wall for a gantry as I intend to mount an air drill to it capable of 400 - 600 lbs of lifting force. Keep in mind their is some monster Hy Def units out there with gantry's that weight 1,000 lbs that cut very true at all speeds.

Steve

PC270695.JPG

[adbuch]

I will not do any flame cutting. I will have a scribe and utilize my Hypertherm 85 with a machine torch. I will be cutting both thin gauge on up to 3/4".

Perhaps I missed it, but what size table are you building? 4x4, 4x8, 5x10 ?? Do you anticipate full sheets of 3/4" or half sheets?
David

[mikeysp]

5x10

[acourtjester]

That is the great thing with DIY you build what you want, I do not handle the size or thickness of material you do. I have not had any problems with the actual dimensions while cutting metal or sign vinyl on the tables I have built.

[robertspark]

I have looked at the JD2 and Shop Sabre machines for inspiration and I am certainly impressed with the build quality; however, I ask myself if it is not overkill for a plasma only machine?

yes

but like vehicles... everyone's got something different and believes theirs is the best or most cost effective or whatever

.... in 10 .... 15 or 20 years you'll probably have a new latest and greatest whatever...

get or build whatever is cost effective and meets your needs.

I am just a hobby user, 1x home built table, gets occasional use, it lives in a garage, is bolted together and designed to be disassembled and reassembled easily with 20T Mod1 rack and pinion 3:1 gear drive
reduction all with nema23 4.2A stepper motors and am882h leadshine drives running linuxcnc and QTPlasmaC with THC, air scribe, 4th axis using a cheap chinese 4 jaw equal chuck 3:1 ratio, 4.2A nema23 drive, also more importantly in my opinion is I am not ransom to and manufacturer, supplier, software. hardware or locked upgrades and firmware.

in my opinion..... (everyone has one and they all will be different).... lightweight and therefore fast is better.

.... more importantly get something that works for you.... you will probably upgrade or replace it in 5-10 years .... like cars you can always upgrade if you don't like it and see something better .... and recover part or all of the cost selling it on plus you have had the benefit of using it.

[mikeysp]

Is it opinion which performs better? Speed/accuracy? Surely there is science. I understand that people have differing needs. Several years ago when I was desiring to build one, I was so broke, I was only interested in the cheapest options that would work. Now, I have a budget of up to $10K and I want a very high quality machine in the area of my budget. I prefer to spend a lot less, but not at the expense of quality. I do not want to build one of several. Surely I can learn the science from others, and get past what works, to what are best practices, what are indifferent options, etc... I am just not clear on the gantry.

Not to rabbit trail, but I read a thread on a guys journey through several controller softwares until he arrived at Linuxcnc. However, it never really identified what were the pros/cons of each, nor whaty made linux best for him, so I am left wondering about it, and won't decide until I am clear at what is at stake.

I have abuilt a few houses based on convention, and some cool sounding idea, and had a lot of headaches and mistakes. I finally discovered building science and best practices, adjusted it to my budget, and now I know how to build a house that is energy efficient, mold free, and very long lasting. While science is not brute fact, it is interpreted data, however, I want the opinion of A is better because x, y, and z. B is 2nd best because w,r, and n.

"I like A", "I use B and I like it " does not give me confidence enough to pull the trigger.

I wish I knew how to ask better questions. Perhaps I should hire a consultant who is the guru, and not trying to sell me something. Anyways, I really appreciate the comments regardless. You have a good group of folks here. When/if I get this build airborne, I will pay it back with a build log here.

Thanks.

-Mike

[adbuch]

To me, the Shop Sabre and JD2 gantries look to be built very heavy duty to support other additional operations - drilling, routing, machining, scribing, etc. Very robust looking.

jd2 gantry.jpg

shop sabre gantry.jpg

By contrast, the Plasmacam gantry consists of a single lightweight rectangular tube. Although it will support marginal routing and scribing/engraving operations, it is primarily intended for cnc plasma cutting and is very light weight to help facilitate rapid acceleration/deceleration while cutting.
In my opinion, the Shop Sabre and JD2, as well as the Avid CNC and some of the others - are extremely heavy duty and I think well suited to a more diverse group of operations.

Plasmacam DHC2 gantry tube.jpg

Plasmacam gantry tube.jpg

I personally own and use several of the Plasmacam DHC2 4x4 tables and they work very well for their intended purpose. Plasmacam also offers the Sampson 510 5x10 table for more money, but using the same servo motors, controller, drive systems, and electronics as the smaller version. I know of many of these 510 tables being used in commercial environments cutting full sheets/plates of 3/4 and thicker material with no complaints from the owners as to their reliability or longevity.

If I were designing my own diy table to be used exclusively for cnc plasma cutting, then I would go as light as possible while still maintaining the required strength for reliable operation.

David

[adbuch]

https://samsoncnc.com/

samsoncnctable2.jpg

[robertspark]

acceleration (speed).

accuracy is not that important..... it's an AIR PLASMA CUTTER, it's not a laser. (or hd plasma)

it's an (semi sharp) metal cutting axe.

if you want precision/ accuracy you would mill it / laser cut it

I am the guy you probably read traveling from mach3 to linuxcnc. I don't have the time to go through the pros and cons of mach3 mach4 uccnc or linuxcnc, the usb smooth stepper, ethernet smooth stepper or UC motion controllers or Mesa hardware, except to say. the ESS is a nice piece of kit but was limited by the developer because you are or were reliant upon warp9 fixing things that did not work or you needed or wanted.

Mesa hardware is totally different .... they give you the source code and you can configure it for whatever you want step and direct steppers or servos, encoders, pwm, I've not tried the other functions but they are there to enable or include.

mach3 is no longer developed..... and it never was bug free or stable (0.66 was not the recommended version for motion controllers).... mach4 was released too early and was just an endless bug fix and development that stuff broke at each release so motion card developers could not keep up with the stable version so their hardware was only compatible with a specific version/ release. I am sure it's now more stable and complete than it was when I last used it. (once bitten twice shy....)
uccnc is good, no real issues except the development stopped during COVID, and went from near monthly bug fixes to nothing ...... they did not do a turning application hence I tried mach3 and 4 again before trying linuxcnc again (I dabbled with it on and off for years but never stuck with it or got my head under the bonnet)

now I have got my head under the bonnet, stuff has clicked and I now see that it's got everything and I am not reliant upon anyone for a stable and developed solution that just works. also adding things in is very easy (once it clicks).

if you have a specific question I'll try to help.

you also need very little in the way of hardware (you don't need a THC, just a means to get an analog voltage into linuxcnc. $70usd = THCAD, done

[adbuch]

Depends on your table setup and your requirements/expectations. Some say that if you can hold to within 0.005" for machined parts, then that is good. It all depend on what you need. Sometimes that is ok, and other times finished dimensions need to be within several tenths. I have specific items I machine (round parts) that require that I hold the finished OD to within 2 or 3 tenths (where one tenth = 0.0001". I have the equipment to do that.

For cnc plasma cut parts, I can hold finished dimensions to within maybe 3 or 4 thousandths of an inch or better. So if target dimension is say 3.750", my Plasmacam table is capable of hitting that dimension pretty closely. Of course this generally requires a few trail runs and adjustments for kerf width along the way. Once set, it is very repeatable. I don't generally need that sort of precision for my plasma cut parts, and I do have many of my parts cnc laser cut and they can hold to within a few thousandths as well.

For most art type stuff, brackets, etc. all this probably doesn't matter.

The OP was asking about choices for his gantry design, and I was simply offering contrasting views between the machine brands he cited and my own personal experience with my Plasmacam tables. Of course opinions will vary.

Some cnc plasma tables may produce "Axe like results", while others achieve much more precise cuts.

David

[mikeysp]

I really appreciate the responses! I am getting closer to firmed up in my mind.

A similitude might be house carpenter to machinist. One says I am a 1/4" out good enough, the other might be out .0001 and say good enough.

One carpenter has walls out of plumb, out of square, and foundation cockeyed, etc... and every thing done afterwards requires shims, trim to hide errors, etc.. This means parts further out of wack than a matching tolerance machine.

So, one could build a SUPER tight tolerance plasma table (like attaching a torch to a milling machine metaphorically) but the plasma arc will always be like a spindle motor and collet with its bearings all wallowed out with such tolerances and it would eb a waste. Whereas, the other end of the spectrum would be to take some untooled Angle Iron and slap some bearings on it. While it might work for a mechanic who uses it to make a bracket to hold a muffler, it would be loosy goosy for someone who wanted to match the accuracy of the table to the capability of the plasma cutter.

In conclusion, for someone who wants to match the capability of his hypertherm 85 with an equally capable table, with no routing ever, a solid frame, with a lightweight gantry and a good rail design weather Hi-Win, hardened V, or cold rolled steel - properly installed/aligned - would make for a well matched machine.

Obviously it is a system, and the other parts will matter too (software, controller, THC, motors, gear reductuiuion, etc...)

I also undertsnad it that cutting speeds will be determined by my Hypeertherm manual and then fine tuned from experience. Where as rapids are nice to have as high as possible if production speed is a factor, and this will be affected by the ability of the design to handle the torque changes and weight of gantry and it's stepper/servo motors.

[adbuch]

Good luck with our endeavor. Let us know how you make out. This is getting all to complicated for me.
David

[mikeysp]

Sorry David. Maybe I should have kept my chain of thought in my head

I really appreciate all your comments, they helped me get closer to the mark.

[SRdesign]

Like a lot of people above have stated, there are so many options as far as electronics, linear rails, gear reduction drives, etc. You can get plenty of opinions and very trusted end user experiences of every different style of system but it is ultimately up to you on how it is built. What I did is look at some of the manufacturers who have been around for a while. Study pictures and videos of their tables to see how they were built. Look at the descriptions of electronics packages on their websites. Then I would come on this website and look at the reviews of the people who actually use their tables, I would also look to see what kind of issues people were having with that table. I looked around a lot in this section of the forum as well to see what kind of parts and electronics were being used. You then have to decide which pieces and parts you want to use for your table, whether you want one or two rails on your gantry, what type of rail, etc. I think I remember watching a YouTube video of a guy using a shop Sabre plasma table and saying that he was limited on his speed when cutting really thin material because of the weight of the gantry, that was a while ago so I could be wrong.

[adbuch]

Like a lot of people above have stated, there are so many options as far as electronics, linear rails, gear reduction drives, etc. You can get plenty of opinions and very trusted end user experiences of every different style of system but it is ultimately up to you on how it is built. What I did is look at some of the manufacturers who have been around for a while. Study pictures and videos of their tables to see how they were built. Look at the descriptions of electronics packages on their websites. Then I would come on this website and look at the reviews of the people who actually use their tables, I would also look to see what kind of issues people were having with that table. I looked around a lot in this section of the forum as well to see what kind of parts and electronics were being used. You then have to decide which pieces and parts you want to use for your table, whether you want one or two rails on your gantry, what type of rail, etc. I think I remember watching a YouTube video of a guy using a shop Sabre plasma table and saying that he was limited on his speed when cutting really thin material because of the weight of the gantry, that was a while ago so I could be wrong.

I have seen the same video of the shop sabre. As I had mentioned above, those bulky gantries can definitely put a damper on your potential acceleration and resulting speeds. That is one of the reasons I chose the Plamacam DHC2 as my "table of choice" - not to mention the servo motors and great software.

In fact, one of the reasons Hypertherm lists two different mechanized cut charts for mild steel using their FineCut consumables is the fact that some of the bulkier tables, particularly those using stepper motors, simply cannot attain the preferred cutting speeds for the FineCuts. Note: FineCuts are recommended for 10 ga. and thinner mild steel.

mild steel finecut.jpg

mild steel finecut slow speed.jpg

For example, cutting 18 ga. at the preferred settings would be 325 ipm, while those hardware limited to having to use the slow speed settings would be cutting 18 ga. at 150 ipm. Quite a difference here, and obviously much more heat and potential warping would most likely occur cutting at the much slower speeds.

For those using control software with the ability to adjust their corner acceleration for circles and/or curves under a specified diameter, then that feature coupled with the lighter servo powered gantry will result in the best of both worlds - slower on corners and fine details, while faster on straight line cutting for better quality cuts with much less heat into the part and thus minimized warping.

David

[mikeysp]

Ok, this was VERY helpful. This was the sort of data I was looking for. At this point, I know I want a lightweight gantry, as much precision as a plasma machine can practically make use of, and the ability to cut at the fastest speeds my Hypertherm 85 would like.

[adbuch]

Ok, this was VERY helpful. This was the sort of data I was looking for. At this point, I know I want a lightweight gantry, as much precision as a plasma machine can practically make use of, and the ability to cut at the fastest speeds my Hypertherm 85 would like.

[SegoMan DeSigns]

One factor to consider when building a table is you do not know what will be available in 3-5 yrs. always leave room for improvements and additions. That is one of the reasons why I prefer bolt on vs weld on, my 6x12 table was built on a budget which dictated I use cold roll profiles as liner rails and chain / sprockets for motion. Go big or go home on table sizing sounds great until you start pricing all the components