just another plasma build and then some :)

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11 Mar 2020 02:45 #159742 by machinedude
i don't think i have the room to make that method work for me Rod.and if i could fit it i would most likely have to relocate the screw height position and that's more than i want to get into at the moment.right now i have nothing more than scrap pieces of material and some of my time as of now. if what i have does the trick then i will run with it.
The following user(s) said Thank You: rodw

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11 Mar 2020 16:29 #159782 by Todd Zuercher
A screw support set up I've seen on some very large commercial machines is to pass the screw through two plastic supports (one on either side of the screw's nut) mounted to bearings on linear way guides then the two guides are connected together with a rod or bar about half of the length of the screw. When the nut moves to the far end of it's travel, it pushes the one support with it, while the other support holds the center of the screw, when the nut moves to the other end it pushes the other support.

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11 Mar 2020 19:22 #159799 by machinedude
I've seen that type of set up and the type Rod is talking about and also variations of what i am doing some better than others.

Todd the type you are talking about is something that would work with my set up easy but the cost is more than what i am doing. so if what i am trying does not work well and get me to where i need to be that style would probably be my next choice. a lot of long linear actuators use that kind of set up too.

the single center drive has space cramped so thin and slender solution are the way i have to go.

if what i am trying works i can have a guide about every foot and a half the whole length of screw if need be. the ball nut itself can factor into controlling whip. the longer the nut the better the screw does. tension on the screw helps some too and even coupling on the shaft can assist whit whip control.

i knew i would have some things to sort out on this screw at the very least from the get go i just wanted to see where i landed first hand and go from there. i think harmonics amplify the whip as well honestly once vibration starts to grow it just keeps getting bigger and the screw reacts.

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11 Mar 2020 21:19 #159809 by machinedude
milled a slot down the center for ball screw clearance on the entry and exit ramp piece and milled a pocket so the whole thing covers the ball nut and housing for the ball nut. ran the assembly up and down the ramp by hand and everything works really well at that level at least.

real test will be under power and with things running faster but i feel pretty good about what i have so far at this point.hopefully i have a winner after this :)

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15 Mar 2020 23:17 #160362 by machinedude
well the whip is under control and this fix works well at keeping the ball screw happy but the plastic i used is not very strong when it comes to being forced up the guide. i think if i switch to Delrin instead of the HDPE i used Delrin will work better.

still can't get much more than 230 IMP out of a printer port. so it's either the printer port or the 4 to 1 ratio i am running at. i feel like i should be able to get more out of the long axis with the test set up i have going? i have the same ratio on the cross beam axis and it does a lot better with the same configuration on the drive. the Z axis is direct drive and i am getting 400 IMP on that axis which is off the torque speed curve chart at that traverse rate and it still won't stall ?

230 IPM is a lot better than what i was getting but it's still slow. i could probably switch my gearing to a 2 to 1 ratio and see if i would pick up my torque at that ratio?

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16 Mar 2020 07:01 #160390 by rodw
If you go Delrin (or Acetal as the non brand name version is called), there is an oil impregnated version specifically designed to be used for bushings. Might be called Oilite or something similar in some markets. Try and find it.

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16 Mar 2020 09:10 #160395 by machinedude
Delrin is just a brand name for Acetal i think. i have a chunk to try it i just had more of the other so i tried it first. should have used the good stuff to begin with :)

i did figure out that 3 of the ball screw supports are more than enough.they really work well for the whip end of things.

i think i might try different gearing on my long axis. i was thinking i would need more speed so i geared up to get better speeds on the Screw but the motors run faster than i thought they would. so if i go with a 2:1 ratio that should give me more torque i think. the acceleration sucks from a plasma point of view. if i can't get the acceleration up this is not going to be very good for plasma. slow acceleration would kill me in the corners i think so it's better to find this out now before i make that kind of investment.

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17 Mar 2020 11:03 #160533 by thefabricator03
I think acceleration with Plasma is relative to what you are cutting. Cutting thick plate does not require high speeds - quite the opposite. You dont see many oxy-fuel machines breaking any speed records.

On thicker plate I can see with the parts closest to the edge of the sheet - the arc lagging from top to bottom. I must get a video of it one day.

Intricate sheet metal is a different story, but if you were just cutting simple squares or just basic parts it would not be a big deal unless you were cutting hundreds and they all needed to be cleaned by hand.

I have tried cutting thinner sheet slower on my machine, it still cuts fine but leaves a bit more slag on the bottom of the sheet.

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17 Mar 2020 12:18 #160545 by rodw
Its actually very hard to video becasue the bright arc blows the video image right out. Try bluetacking a welding glass in front of the lens.

Even on 8mm though, the top part shows marked striations which are evidence of that lag on the bottom of the sheet.

Image stolen from my spaceship build thread. (p 39 or thereabouts)

The striations on 16mm really show that lag.

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17 Mar 2020 13:35 #160557 by machinedude
first off i hate hand work so dealing with a lot of dross is not something i want to deal with. second off i could see a need for being able to do thin sheet. thin material runs faster and corners are more likely to blow out if you cant
keep the speed up in the corners.

i ordered a different set of timing pulley's to see if i can pick up some torque there. They only cost around $30 to try so that is not going to make or break the build. the Z axis pretty much runs at max with out issues but it's 1/5 of the weight of the whole gantry. the motors are listed up to 2,250 RPM so for me to get 400 IPM with a direct drive it's running maxed out. so if i can get more out of the long axis by switching the gearing it seems like it's worth checking out. the way the drive is put together it's a simple modification on the long axis.

it's already on it's way but by the looks of things it's coming from over seas this time so i won't see it for a few weeks probaably?

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