have you ever seen ?

[machinedude]

I had this idea to make a bar or tube feeder for a small plasma table. the idea was to automate the clamping on a rotary axis so you could basically cut a 24'length on a 4.5' table if you had the need. 24' for me would probably be too much to handle but 12' or half bars or tubes might be more practical for me.

i spent a lot of time looking for information on the mechanical design aspect and have already started to build a R & D version to see if i can bring it to life but it's pretty complex as far as designs go and a ton of work to build to say the least.

i have yet to see anything like this and was wondering if it is even out there? so has anybody ever seen automated self centering clamping that can be programmed?

[adbuch]

My NakaMura Slant 1 cnc turning center has an automatic bar feeder/puller. It is an attachment that goes into one of the tool positions on the turret. The way it works is that under program control - the attachment grabs onto the material, the hydraulic chuck then releases the jaws, the material is pulled out of the chick in the +Z direction to a programmed position, the chuck closes, and the attachment releases the material and retracts to the home position. The actual pulling of the material is accomplished by moving the "carriage" in the +Z direction.

Perhaps show us what you have in mind and I will put on my ME had and take a look.

David

[machinedude]

basically what you described with the exception of it being hydraulic in my case i'm starting with pneumatic clamping. so out of the gate i will have some weight restrictions but this is not a commercial machine and maybe advanced hobby level. but eventually a combo 2' x 4' ish table with the rotary off one side with the bar feeding axis running parallel with one axis. one end is a fixed steady rest, and the other end will drive the rotary and linear motion end of it and both will clamp independently.

right now my bore is 5.5 inches so if it fits shape is not an issue with custom jaws. the biggest speed bump is a hollow body rotary union which is what i am working on now to test the concept.

i would post a screen grab but it does not show much detail since the cover hides most of it.

[Deezl Smoke]

This is not on a table, but is this what you are looking to do?
https://www.youtube.com/watch?v=xMb9XZjK6m0&t=6s
I still get emails from them as I inquired about this machine when I bought my mandrel bender. But it would take a lot of tube business to pay for it, so I opted out for now anyway.

[adbuch]

Let's see what you have. You can always take the cover off so we can better understand the details of your design. There was a design for an adjustable self centering pipe chuck shown in a recent post. Perhaps you could apply this concept to your project. Maybe replace the rollers with jaws for clamping and add power actuation for the opening/closing operation.

David

https://plasmaspider.com/viewtopic.php?p=244148#p244148

IMG_20250112_085004~2.jpg

[machinedude]

i have seen quite a few designs that have the rollers but what i have seen has all been manual control of the clamping. the A 400 is one i have looked at before. most use a self-centering 4 jaw at the rotary end. that's my back up plan but i would rather have clamping automated. i'm at work at the moment but can get into it more a little later.

[machinedude]

missed the part about the lathes. we have lathes with 2 spindles at work that can act like a bar feeder. that's far more complex than what i want to do. they can sync and grab the stock while running to index stock. i watched the A 400 video again and don't see the need for two independent rotaries.

the mechanical end of this is not so bad for me i have close to 40 years under my belt making stuff the tricky part is making it with the equipment i have at home and doing in such a way as not to break the bank in the process.

[machinedude]

somewhere around 3 weekends of working on this i have the rotational aspects of it sorted out. So, if i can get it to seal and direct air in the right places the rest is downhill. Well at least until i get to the other side anyways. That side is a bit more complicated. I still have a ton of work on this side to finish before i even move on to the other side. i have to make the base and feet to mount this to and have to dill some side holes to tap for fittings and cut the glands for the seals. i need some strain relief for the air lines as well. lots of work to do yet

steady rest.jpg

[adbuch]

This looks nice, but I can't tell how it will work. You picture looks very much like a Porsche 911 rear brake rotor.
i will look forward to learning more about your project.
David

[machinedude]

the outer ring is fixed, and the center rotates. the hub in the center rotates with the center but the outer free spins so the air line can stay stationary. that part is the hollow body rotary union and also where the seals get placed. if that help make sense of it

[adbuch]

That helps some. I will wait to see your final design for a better understanding.
Thanks,
David

[Deezl Smoke]

Wow. Just wow. Nice bit of work you've done.
So the seals, do they have to seal under air pressure while rotating? Because the air will clamp, then cutting action, then release air, move tubing, and apply air again. Correct?

[machinedude]

yes the seals rotate and would be what you call a dynamic sealing. ok at lower speeds on a high rpm spindle no way most likely.But the idea is to be able to unclamp and clamp each one individually so it can act as a bar feeder. Everyone i have seen is just rollers that the material just gets pushed through by the other end usually using a 4-jaw chuck.

[Deezl Smoke]

What seal type are you planning? And have you done any calculations to the load the seals will put on your motor while under pressure?

[machinedude]

it really should not put strain on a nema 34 with reduction. plus, everything is locked in place with the rotating element. things have to be tight and right for it to work. things have to be concentric and round to around .0005 of an inch. as for seals special shaped Oring seals for dynamic applications is what i decided to try. this is just a proof of concept build at this point. nothing ventured nothing gained is how i look at it at the moment. i have never seen it so i decided to try and build it i could fall on my face

[Deezl Smoke]

it really should not put strain on a nema 34 with reduction. plus, everything is locked in place with the rotating element. things have to be tight and right for it to work. things have to be concentric and round to around .0005 of an inch. as for seals special shaped Oring seals for dynamic applications is what i decided to try. this is just a proof of concept build at this point. nothing ventured nothing gained is how i look at it at the moment. i have never seen it so i decided to try and build it i could fall on my face

I agree with you outlook 100%. Ya gotta try.
So on the o-rings, I had some bad issues going straight in with just o-rings and no back up ring. Have you considered incorporating an o-ring back up ring of some sort to reduce the pressure on the o-ring surface at the mating point while air is applied? Usually the back up ring is a composite material so no wear damage to the seal surface. Kinda like a hydraulic piston seal, but rotational in your application.

[machinedude]

i seen some info on backup rings but i'm not sure if they would help all that much? between a light fit over the shaft and not much of a gap between the inner and outer walls of the union it would be hard to extrude the O-rings if the clearances are good and the stretch and compression are right. if i have trouble then that might be an option for a solution but i think the glad should be enough to start with.

[PlasmaDon]

Standard CNC lathe chuck configured for thru bar feeding.
Both pneumatic or hydraulic actuation.
Look at a website like worldwidechuck.com

[machinedude]

The catch to it is the bore size. once you get past a point the prices of things just go through the roof. if you want to do 4-inch square tube you need around a 6-inch bore to pass it through. i have seen lots of good ideas for manual roller guides that can be done cheaply to do much larger sizes but this idea of mine was interesting to the point i was eager to try and do it on the cheap side to see if i could make it work. this is not something new as far as tech goes just something i have not seen on plasma or at least on the low-end side of price point.

[Joe Jones]

Have you ever slipped into a car inner tube and inflated it?

Imagine a doughnut of a round rubber tube. In its relaxed state, it has a six inch center hole. Now you slip a length of extruded material through it. It can be round, or rectangular, or triangular, or hexagonal, or whatever. It rests on a roller that temporarily supports the weight.

Now you inflate the tube, and it compresses around the extruded material. The air pressure against all sides of the tube would equalize, and the extrusion would naturally end up in the center of the inflated rubber tube. As the apparatus that holds the rubber tube rotates, the extrusion would rotate with the tube, with equal air pressure on all sides. Cut the end, and then deflate the tube to advance it. Reinflate, and repeat the process.

It seems simple. I would have to build one for proof of concept, but I have WAY too many other projects started already.

Joe

[machinedude]

interesting concept but a different direction than i am heading I have double rod pneumatic air cylinders coming in later today that i am going with for clamping. they have 2 points i can attach custom soft jaws to with M8 screws. by design you already have the center line in one direction but i am betting since they are the same size the center should equalize and find the center in the other direction. with air cylinders you know how much force you can get just by knowing the bore size and supply pressure. So things are a little more predictable. One other issue that i seen coming is grounding with a rubber bladder i am not sure how you would get around that part? But in my case i will have to add a ground strap to the jaw and remove the anodizing since anodizing acts like an insulator. So i will be keeping an eye on that as i go. i would guess trying to ground a rotating part would be no fun

[Deezl Smoke]

interesting concept but a different direction than i am heading I have double rod pneumatic air cylinders coming in later today that i am going with for clamping. they have 2 points i can attach custom soft jaws to with M8 screws. by design you already have the center line in one direction but i am betting since they are the same size the center should equalize and find the center in the other direction. with air cylinders you know how much force you can get just by knowing the bore size and supply pressure. So things are a little more predictable. One other issue that i seen coming is grounding with a rubber bladder i am not sure how you would get around that part? But in my case i will have to add a ground strap to the jaw and remove the anodizing since anodizing acts like an insulator. So i will be keeping an eye on that as i go. i would guess trying to ground a rotating part would be no fun

You'll have no issues grounding a rotating part. You already exhibit the thought processes needed. You can ground through bearing. It is fine to do so when needed. Just run some preload on the bearing, and pack it with grease. Doesn't have to be dielectric either. But you already have plenty ideas for grounding, just throwing that option in if it is one that can work.

[djreiswig]

For grounding, use a braided ground battery cable wrapped over the tube and tension it with a spring.

[machinedude]

grounding should be easy to solve. the biggest thing is knowing you need a good connection. the air cylinder bodes are anodized and the pistons on the inside are insulated with the O-ring seals. So you need the ground strap to bridge the gap, so you have continuity between the clamped part and the steady rest, so you don't have to mess around trying to ground something spinning. i did not think about it at first but caught it later in my thought process after watching a video seeing what someone did for grounding and thinking to myself there has to be a better solution

the way i plan to do things is work a small gap for clearance into the soft jaws when fully retracted so the jaws only have to move around .1 to clamp. that way i can just add a small, braided copper ground strap with a little extra slack so nothing gets strained. once the connection is bridged i can add a clamping point to something stationary to get easy grounding and cable management. simple continuity checks with a meter to confirm everything is good to go at that point.

[machinedude]

the air cylinders came today so i took a quick picture of them just setting on the back side of this clamping steady rest project. i have to make riser blocks and then attach mounting plates to those so everything clears the out ring since that part is stationary. you can see the ports that supply the air to the cylinders. i kept it simple and will slave the air supply for the clamping and slave the other side as well. i am taking a bet that they will equalize in the center and figured it would give less places for leaks. lots of work to make this no doubt.

clamping steady rest 1.jpg