robertspark Posted October 16, 2014 Author Share Posted October 16, 2014 For Robert! Plasma IGUS.jpg I also added a micro-switch on Z. Some people touch the tip of the torch on to the plate being cut, then back off a suitable distance at the start of each cut instead of using torch height control. Since a microswitch only costs 50p - this is a more cost effective, if less cool strategy. Plasma Micro 1.jpg Plasma Micro 2.jpg Si Oh Si, I see what you're doing now, I didn't realize you were using a floating head (didn't know one such existed, until doing a search online) Interesting email I had with hypertherm about my plasma, basically the manual lists the optimum velocities at 25 Amps, which is 35% duty cycle (3 1/2 mins run per 10 mins for those who may not know about duty cycle, applies to welders too). I asked what the reduction in plate thickness and cut speed should I reduce the ampage to say 20A (60% duty cycle) or 17A (100% duty cycle), basically I was told that there was no had and fast rule, more trial and error, but the technical bod felt it would be proportional to the ampage reduction (i.e. 25A->20A = 20% travel speed reduction & 25->17A = 32% travel speed reduction). May be of use to someone. Likewise the guidance is for pierce height (from hypertherm) to be roughly double the cut height recommended by the manufacturer (1.6mm in my case), therefore pierce at 3.0 to 3.2mm (other manufacturers probably quote different), again may be of use. 1 Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 16, 2014 Share Posted October 16, 2014 I found this recommendation for setting motor tuning after a little searching, it doesn't sound particularly scientific but does sound reasonably sensible. ' It's really impossible for anyone to tell you what the correct settings for your machine will be - every machine is different. Just start with a low acceleration - like 0.5, and crank the max speed up until the motors start stalling at the top end. Back off perhaps 10% from where they stall. Then start moving acceleration up, until it stalls on acceleration, and back off on the final acceleration setting. Then, run the machine hard and make sure it really works reliably under more "dynamic" conditions. ' I'm assuming that X wiill have the slowest acceleration rate probably followed by Y then Z Quote Link to comment Share on other sites More sharing options...
simonr Posted October 17, 2014 Share Posted October 17, 2014 Best option is to write a program that cycles one axis back and forth a few dozen times at rapid speed (G0). ;Test X Axis G0 X0 Y0 Z0 ;Measure starting point with vernier ;Repeat the next bit a few times G0 X500 G0 X0 ........ ;Measure end point with vernier and compare to start measurement Measure the position of that axis relative to something else using a vernier, run the program and measure again at the end to see if it has lost steps. If so, reduce speed / acceleration - If not, increase speed / acceleration until you find an equilibrium where the machine moves as fast as possible, maintaining accuracy. Si 1 Quote Link to comment Share on other sites More sharing options...
robertspark Posted October 24, 2014 Author Share Posted October 24, 2014 update .... building the driver case / enclosure Question, what plasma cutters are / is everyone else running, how well do some of the cheaper (cost effective) chinese ones work on thicker stuff ..... do they work on a CNC without HF (high frequency) start / pilot? I was wondering about cutting stuff thicker than 6mm which seems about the recommended limit for cut on mine (9mm severance). Not sure how realistic some of the chinese 50A ones are running off a 13A plugtop single phase.... or is that a bit of hype? Quote Link to comment Share on other sites More sharing options...
Lewis Posted October 24, 2014 Share Posted October 24, 2014 I have a Chinese 50amp single phase machine running on a 16amp blu commando plug, it replaced a Chinese 40amp which we did try running off a 13amp plug but it ate fuses for fun so we swapped the 16amp plug back on. I've cut m18 bolts with the 40amp and it didn't trip the breaker Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 24, 2014 Share Posted October 24, 2014 I'm still designing my carriages but I'll be using my R-Tech 50A HF plasma cutter, although it's HF I know of at least one diy builder using this plasma cutter succesfully and I believe r-tech themselves also rebadge this cutter to sell with a cnc table. From spec it should clean cut 18mm and severence 24mm, I have used it to cut 3/4" plate succesfully (but slowly) I have it connected via a 32A commando plug. Quote Link to comment Share on other sites More sharing options...
Cynic-al Posted October 25, 2014 Share Posted October 25, 2014 I caught my dog chewing a plastic clothes peg last night, the only bit I recovered (for now anyway) was the spring which looked remarkably like the one being used in the video above as a belt tensioner, could be worth a try as they're mega cheap! Quote Link to comment Share on other sites More sharing options...
robertspark Posted October 25, 2014 Author Share Posted October 25, 2014 clothes peg springs: Yes, I did think about using one of those, the catch is the belt width... finding one in my case 20mm wide, I've now had some made (or being made), I'll post some pictures when I get a chance, seem to work a treat, but I've not driven my steppers yet. chinese plasma / cheaper machines: Those R-tech plasma machines look similar to a number of other chinese ones rebadged, good to hear that people have had good results. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted October 25, 2014 Share Posted October 25, 2014 I've used a clothes peg spring to repair a broken door pull spring before now! They do work well, and if good quality are stainless Quote Link to comment Share on other sites More sharing options...
simonr Posted October 28, 2014 Share Posted October 28, 2014 I guess it doesn't matter if it doesn't span the whole belt - defo worth a go! I had a pallet turn up from the Laser Cutters today! A big jig-saw puzzle! Hopefully the box section will turn up tomorrow so I'll be able to build the frame at least. Still waiting for some parts from China (Belt Pulleys mainly) but I'm pretty close now to seeing if it works! Si Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 28, 2014 Share Posted October 28, 2014 That looks all very nice Do you think you'll be needing that rawhide adjusting tool in the picture? Quote Link to comment Share on other sites More sharing options...
Lewis Posted October 28, 2014 Share Posted October 28, 2014 I nice to see that even millionaire genius inventors cannot keep their bench tidy 1 Quote Link to comment Share on other sites More sharing options...
simonr Posted October 28, 2014 Share Posted October 28, 2014 Naa - the hide hammer is just for 'personal enjoyment'! Si Quote Link to comment Share on other sites More sharing options...
robertspark Posted October 28, 2014 Author Share Posted October 28, 2014 I nice to see that even millionaire genius inventors cannot keep their bench tidy Haha Don't matter how big the bench is it still ends up with a 2x2ft working square. Nice to know we all in the same boat Quote Link to comment Share on other sites More sharing options...
robertspark Posted October 28, 2014 Author Share Posted October 28, 2014 I nice to see that even millionaire genius inventors cannot keep their bench tidy Haha Don't matter how big the bench is it still ends up with a 2x2ft working square. Nice to know we all in the same boat 1 Quote Link to comment Share on other sites More sharing options...
simonr Posted October 29, 2014 Share Posted October 29, 2014 I assembled the laser cut bits this evening. The other steel arrived today - but I've yet to cut it up. All the bits went together OK. A couple of the bolt heads are difficult to get to unless you assemble the bits in the right order - but easy to figure out. The flexible coupling for the Z axis turned up - though I've discovered the one I ordered is designed to fit an 8mm shaft on the stepper motor - but the shaft is 6mm. I'll machine a little tube spacer - but I'll change it on the bill of materials for next time! I'm still waiting for the belt pulleys - other than those I have everything to run it. Si 2 Quote Link to comment Share on other sites More sharing options...
robertspark Posted October 29, 2014 Author Share Posted October 29, 2014 Congratulations! You done your driver box? Quote Link to comment Share on other sites More sharing options...
simonr Posted October 29, 2014 Share Posted October 29, 2014 Not yet. I bought a cheap USB motion controller on eBay. Same deal as Smoothstepper but £25 or so rather then £160. If it works decently then it opens up a wider range of PC's to drive it with. If it works, my plan is to get an all-in-one touch screen & PC which generally only have USB. Then I can mount the screen, drivers & power supply in a single box. If it doesn't work well - then the drives & power supply are going in an Ammo tin with a separate PC & screen. I started drawing up a simple table the cutter could sit on - but my plan is to cut the table with the plasma itself as it doesn't need to be that precise. I was thinking about folding or plug in legs so the whole thing packs down when not in use. It would be nice to use the plasma to cut bits of itself! Si Quote Link to comment Share on other sites More sharing options...
simonr Posted October 30, 2014 Share Posted October 30, 2014 Exciting evening! Nick Watts cut the steel for me (His saw is a lot more parallel & accurate than mine!) Thanks Nick! I've assembled the Z-Axis first to see how well the Nylon rollers run on the corners of the box section - and they are smooth as! The location is surprisingly good so laterally & torsionally it is very solid. It bodes well for the X & Y axis which are better supported (5 rollers instead of 3). Sorry the photos are a bit crowded on my untidy bench! You get the idea though! Charles - I've measured the tube and testing in several places, the dimension corner to corner (which is what I'm interested in) is only +/-0.05mm and I can't see any twist at all over 1.2m (longest length). I was a bit worried that this might be a problem - but thankfully it doesn't seem to be. I wonder if being thin wall helps? Si Quote Link to comment Share on other sites More sharing options...
robertspark Posted October 30, 2014 Author Share Posted October 30, 2014 Looks good Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 30, 2014 Share Posted October 30, 2014 Good progress and very professional looking, can't wait to see it's first cuts. My build is going to take a bit longer due to .... erm decorating Quote Link to comment Share on other sites More sharing options...
simonr Posted October 31, 2014 Share Posted October 31, 2014 Perhaps you could convince your partner that this is an automatic decorating machine - you hang it on the wall and it cuts 'designa' patterns in to the surface with that fashionable 'burned' look? Si Quote Link to comment Share on other sites More sharing options...
robertspark Posted October 31, 2014 Author Share Posted October 31, 2014 I wonder what it may be able to do with a paintbrush and wheels to move its self around the room automatically ..... Wake up in the morning and the paintings done (could be on to something here) Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 31, 2014 Share Posted October 31, 2014 ...... I'll be sure to suggest it to her .... lol I'm sure I will sneak in some plasma cnc building, who needs sleep anyway? Quote Link to comment Share on other sites More sharing options...
simonr Posted November 1, 2014 Share Posted November 1, 2014 Well, bit of a mixed day today! I assembled the whole frame and it works pretty well. It's not totally rigid (has some elasticity in the corners), but good enough I think. It has turned out pretty light at maybe 6kg including the motors etc. Light enough to pick up and hang on the wall when not in use. Unfortunately I found that the little plastic rollers were too flexible to give enough rigidity in some places. They work fine on the X axis, but the Y & Z were hopeless! The rollers were not helped by having the cheapest, nastiest bearings inside them - which have a fair bit of axial play while at the same time being quite stiff to turn. This morning I was thinking I would have to start again - but then thought, if it's only the rollers that are the problem, I might as well make some & see if they are any better. Nothing to loose! I have machined a load of aluminium rollers instead - and asked for a quote to make batches of 100. These work 100x better! I'll order some of these which appear to be the same - see if they are any better! Hopefully the combination of machined rollers & the bearings will cost less than the plastic rollers! They came in at about £5.50 each and I can't imagine the aluminium bits will cost more than £4.30 (which would be the break even point). I'll take & post some photos later. Si Quote Link to comment Share on other sites More sharing options...
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