I would either bolt down some thinnish alu plate on each member and then skim them all level, or pour more epoxy on the members so they self level. But that means making a framework for the epoxy to travel between members.
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I would either bolt down some thinnish alu plate on each member and then skim them all level, or pour more epoxy on the members so they self level. But that means making a framework for the epoxy to travel between members.
Epoxy sounds a bit too complicated for something so simple and you'd have to confirm the frame was adjusted to make the plane of the rails orthogonal to local gravity or it becomes pointless.
I'd go with the shim and skim. That cannot fail to put the plane of the base parallel in all directions to the plane which the spindle moves which is what you really want and will minimise the thickness of material you need to skim off the final, sacrificial surface.
Out of interest did you put a moat across the two rails when you poured it?Quote:
I took the a rough height map with a DTI clamped to the Z. As expected from bringing the rails into plane with laser and epoxy I have around 1-1.5mm total error (this was the frame error before pouring epoxy). The cross members of the frame are also not perfectly in plane and would require a little shimming under the bed.
I'd rather have the bed closer to planar that this, although the eventual spoil board skimming will fix it, so I'm contemplating attaching some shimming material to the cross members and surfacing this then bolting the bed plate down on top.
I would use epoxy metal paste. Use levelling grub screws in the bed and adjust until planer, then remove and skim all the surfaces with a lite coating of epoxy putty then put plate back on and tweak it out any error from lifting etc.
Tape the bed where it meets the epoxy and when dry you will be able to remove bed.
It's not possible to skim the whole surface using the machine because plate is the full size of the base so cannot skim the portion under the gantry.!! Only way this could work is if the plate was the actual cutting size.Quote:
Originally Posted by Kitwn
Obvious when you point it out!:stupid:Quote:
Originally Posted by JAZZCNC
I like the grub screws and epoxy putty idea, but might it be better to use ordinary bolts instead? It would mean a slightly thicker layer of putty but it would allow you to adjust each bolt with an open spanner while the gauge is on it's head rather than have to measure, move the gantry away to adjust, move it back to measure, move it away to adjust again etc.
No point really and you want to be measuring off the bed not the bolt head. A M3 or M4 socket cap grub screw is easily adjusted thru the hole and is small enough not affect the bed too much.Quote:
Originally Posted by Kitwn
There are several ways to do the same thing and it depends on how your planning on using the bed regards fixtures etc. The main point was Epoxy putty works good for this application, it could easily be car body filler(Bondo to you upside downers) if your on a budget...Lol
I was thinking the grub screws would be in the frame, not holes drilled in the base board. Slowly but surely the lights come on.
Thanks for the ideas guys. I went ahead and epoxied some 2" x 1/8th aluminium strip to the 3 cross members that are machinable from the gantry. There is around 60mm outside each of these which will be shimmed manually. The rear cross member cannot be machined as it is under/behind the gantry as Jazz says, so this will get manually shimmed as well. Quite easy to do with a DTI n the Z as 90% of the bed plate is supported by the milled strips,
Attachment 28459
So the exciting bit was getting the machine to machine itself, first time it has cut anything:
https://youtu.be/mnwhJR-eVZg
Finish was superb for chewing gum grade aluminium, thickness of thinnest final shim is ~1mm.
Attachment 28460 Attachment 28461 Attachment 28462
I used an 8mm 2 flute carbide bit, there is no scalloping which means the head is in pretty good tram (I can't tram it until the bed is on). I ran the tool path twice, initially to bring all 3 strips down to height then dropped the Z 0.1mm for a finish pass.
Hi Clive, yes there was a moat, I put it outside of the frame at one end. The rails are planar within 10um, I checked them with my laser software. Or at least they were when I fitted them, they have probably drifted a bit as I've hoisted the machine around the shop a couple of times since then. I will recheck them at some point.Quote:
Originally Posted by Clive S
I didn't post anything about how I did the pour but there are two important points I'd like to pass on to get the best result,
1. As per Boyan's findings the moat should be outside the frame, close to the same cross section as the rail support epoxy and the pour should extend beyond both ends.
2. You must use non-absorbent material for the moat and dams, anything else and non-linear capillary action into the material will mess things up. I used 10mm pvc angle for the dams and pvc trunking for the moat. The dams were stuck to the frame with thin toffee tape which worked well (didn't leak) but was a pain to get off.
Attachment 28463
Time to fix the bed down. I want to finalise the work holding at the same time. I have a few choices,
1. Drill and tap a grid of holes in the plate and bring these holes up through the spoil board,
2. Just drill and tap the spoil board (pvc foam) creating blind holes.
3. Cut t-slots into the plate and create narrow planks of spoil board between them (I would need to get a special bit to cut the t-slot),
4. Create t-slots from planks of spoil board, not sure how strong they will be.
T-slots are probably more work but less tapping, what do people think?
I'd go with a mixture of T-Slot Track in the Spoil board around the outer edges and a matrix of Tapped holes.
The T-slot allows quick and easy clamping of large pieces.
The Matrix of holes allows you to clamp small parts easily and just about any where on the bed and nearly always means you can find a place on your part to clamp.
The pain of tapping all those holes is worth the effort IME.!! . . .
Cool, any suggestion on the pitch of the matrix? I was thinking 150mm to limit the tapping...
Also would you tap the bed or the spoil board?
No 150mm is way too big, 75mm would be max I'd go with, 50mm better. Don't be put off by the tapping, the thought of it is worse than the doing. Plus you don't have to tap every hole straight away, could even just tap every other hole and use the others for dowel pins for fixture guides etc. This is where a matrix really comes into it's own because it's very flexible.Quote:
Originally Posted by devmonkey
Tap the Bed not the spoil board. You'll be cutting into the spoil board and slowly surfacing it away.
I have M8 tee nuts in the underside of my plywood baseboard with a drilled MDF spoilboard on top but I doubt you will allow anything so porous or flexible onto your machine. My spacing is 100mm and it's definitely too large.
One thing to consider is making the effort to get the holes on exact multiples of 50 or 75mm from your zero reference in both X and Y. You probably will drill them here anyway but this makes it easier to plan the layout of a job if you want to drill fixing holes in the workpiece, dedicated spoilboard or a jig. I say this because I made the mistake of drilling the holes, fitting the tee-nuts and then turning the board over to screw it down which means the grid is not as perfectly aligned as I would wish. We live and learn, it'll get fixed one day.
I actually don't agree with the above. I used two moats about a third from each end. But what is a must, the epoxy must be wide enough to all for the mucus (or whatever you call it) on each side and use the very slow epoxy.Quote:
1. As per Boyan's findings the moat should be outside the frame, close to the same cross section as the rail support epoxy and the pour should extend beyond both ends.
I was going to drill the fixture holes before finally fitting the bed, but I agree it is better to do it afterwards once the machine is properly aligned. I haven't squared the gantry yet, nor properly defined zero. Will get the bed fixed to the frame in its final location, clamp on a sheet of MDF on top to square the gantry, define zero then finally drill the fixture holes.Quote:
Originally Posted by Kitwn
I'm also toying with the idea of redefining my long axis as Y and the gantry axis as X so it lines up with the natural way of looking at it from the front and the axis orientations match the DDCS buttons, otherwise I'm going to make a mistake. I would define zero as front left.
I have drilled and tapped the bed and frame, and bolted to the locations where I had fixed and milled the aluminium strip. Reads within +/- 0.01mm everywhere in this region and there is a 0.02mm droop towards the as yet unsupported rear end. I think rather than try and shim the unsupported bits with shim material I'm just going to squirt some structural 2 component polyester resin in there, it is close enough and I will just make it worse trying to shim normally.
Attachment 28464 Attachment 28465
I guess whatever works for you.Quote:
Originally Posted by Clive S
I did some tests under the microscope before I did the actual pour, the epoxy shrinkage phase occurs after it has setup too much to freely flow and find level, this (as Boyan determined) is what causes dips around dam ends and bridge joins. I used West's 105/209 and the shrinkage phase starts after about 1 hour by which time it is getting too viscous to re-level itself. The way I saw it is the bridge is only effective before the shrinkage starts and after it starts you want the area x-section of the epoxy you want to keep to be as consistent as possible meaning you have to extend it past the ends of the machine and you want the bridge to be connected to a part you don't want to keep as it either it will pull from the sides or the sides will pull from it. Either way it doesn't matter as you are going to cut this bit off.
The microscope method was stolen from the "Dam Busters" use of angled lights on the wing tips to determine they were the correct height above the water to drop their bombs. You point a laser pointer at an angle to the surface, focus the microscope directly down onto the point where the laser hits the surface and as the surface height changes the dot will move, magic ;-)
In the picture you still have the protective coating on the plate so you can't trust those measurements if you did it with that still on.?Quote:
Originally Posted by devmonkey
Regards the Epoxy and bridge etc then I've probably done more pours than anyone here, I've lost count of how many but it ranges from Medium and V-large, my experience is between both you and Clive. I agree the moats are better outside the frame but you need them both ends of the machine. Also, make the moats lower than rail surface as this seems to help the flow. However the most important I find is the temperature, keep the temp on the low side of what's recommended as it slows the curing process and gives it more time to level. The only tricky bit is it's a fine line between just right and too cold and it not setting correctly.
The covering is tight and uniform so I think I can trust them enough, I DTI'd the milled shims first which was zero everywhere, happy that my +/- 0.01mm on the top is a mixture of error from the covering and the plate itself. Anyway doesn't need to be perfect as the spoil board will take up any error, if I need a very flat part for bolting a vice to I will skim the aluminium bed, I left the bolt heads low enough to do this.Quote:
Originally Posted by JAZZCNC
Bed is now fully fixed. I reckon it is within 0.02mm total error, not that I really trust this digital DTI.
The rear cross member and the outer edges of the other cross members that did not have the milled shim were done as follows. I laid some narrow strips of closed cell self-adhesive glazing rubber either side of each bolt hole. Then I re-placed the bed and tightened the central set of bolts down hard onto their milled shims. I then indicated the entire bed adjusting the outer bolts to zero, the glazing rubber provided a bit of resistance to bias the bed plate high so the bolts had something to tension against. Finally I got under the machine and injected some construction resin into the gap, this set hard in a few minutes as it is so hot today, it is basically bondo in a cartridge.
The bed plate had a very thin film of WD40 on it to act as a release so hopefully it will be possible to get it off again should I ever need to., not sure the resin sticks well to the shiny aluminium plate anyway.
Attachment 28469 Attachment 28470 Attachment 28471
This is the very last time that bed will look so nice!
EM806 question.
All the documents state that the alarm output is 'active high' by default and that 'active high' means
"Active High
means high output impedance for drive error and Active Low
means low output impedance for driver error. "
When I connect to the drive over RS232 it indeed states it that the alarm is active high. However it is behaving opposite to the manuals, rather it is high impedance normally and low impedance in error, I verified this by stalling a motor. I have now configured it to active low which allowed me to daisy chain all the alarms together - they are conducting to ground until a drive goes into error or the fault wiring is broken.
So my question is why is the behaviour opposite to the manuals and should I be concerned that things like the step edge setting may also be reversed? Is the manual just wrong and 'active high' means their logic output is high in error driving the base current on the NPN which then conducts, i.e. has low impedance?
I've had this many times with the AM882 and the EM806 and it's a random thing, it's like they must put something in backward...Lol
Regards the Step edge then I'm not so sure because while I've had many drives be on the wrong side of the edge I never actually checked which was at fault, the controller, or the drive. I just do a quick back n forth check with g-code and if it drops steps then flip it over. I do this on every machine regardless if the drive and controller say they match or not.!
Thanks for clarifying Jazz. All 4 drives I have here behave the same way, opposite to the manual. Possibly there are multiple versions of the firmware floating around.Quote:
Originally Posted by JAZZCNC
Will do the test for step edge, does it lose a step everytime the axis reverses, i.e. I should be able to test it as creep on a DTI at either end of the stroke?
Yes it drops a step every direction change. I just zero the axis put DTI on it and do 200-300 small G0 moves, 5mm or so, with the last move back to zero.Quote:
Originally Posted by devmonkey
I squared the gantry today. I used the method of equalising diagonals. First I had to make a measuring stick:
Attachment 28479 Attachment 28480
Then I had the machine drill 4 holes in a rectangle and inserted dowel pins, zero'd the DTI on one diagonal then measure the error on the other. The arduino board I made for axis squaring only had 8 bits of step offset. This machine uses 1610 screws and 16x microstepping so 8 bits represents 255*10/(200*16) = 0.8mm of software correction to the limit switch. Therefore I had to get it close first by moving the proximity sensor targets first, I got the diagonal error down to 0.32mm.
Fine tuning squareness was then done by changing the offset in the arduino code. After lots of messing around trying to calculate the gantry error angle then the actual number of steps to offset one switch I gave up. I just drilled holes with offset at zero, then with offset at 255, then interpolated the two errors to get the 'correct' offset (note this is not the correct way to do this but it works well enough over these very short distances). Plugged this into the software and low and behold:
Attachment 28481
0.01mm error over ~1000mm diagonals. Square enough for now, it is repeatable. Can't do better than that without a much better DTI and some measurement of backlash.
Annoying sources of error whilst doing this were 1) a dowel pin that got scratched up pulling it out with pliers, 2) not having the DDCS home twice, this made it a little more consistent, don't know why.
I also noticed that the EM806 stall detection is not working for a stalled start, it works fine if you stall a spinning motor. Is this something I can tune or is it just a limitation of sensorless stall detection?
I think that stall detection only works if the motor speed is greater than 300 rpm - so won't detect a stationary, stalled, motor. Unfortunately...Quote:
Originally Posted by devmonkey
Yep Stall detect only works above 300Rpm and yes it's limited in its accuracy and reliability.Quote:
Originally Posted by Neale
Fair enough, it was a rather artificial scenario caused by me not plugging in the signals to one of the motors on the dual axis whilst still powering it (so the driver had it locked), the other motor stalled obviously.Quote:
Originally Posted by JAZZCNC
Nice job Joe. I think most of your readers would consider that 'square enough for now' :thumsup:Quote:
Originally Posted by devmonkey
Just in the process of rigging up some dust extraction which is going well, but I also need air assist for aluminium chip removal. I have a very loud compressor I don't want to use, can anyone point me towards something quiet that has the required flow rate and pressure (apparently some people use pond air pumps??) for blasting chips out of deep pockets?
I've also seen these small plastic fans you can slide onto the cutter but I can't imagine they can blow chips out of deep narrow pockets.
I found a little side channel blower in fleaBay for about £60 - with a little nozzle it blew chips everywhere, so much so that I had to throttle it back a bit. If you're tempted to go the same route just be aware that those things come in different flavours of pressure and volume delivery, the one I found did quite a reasonable pressure, ~280mBar IIRC.
I find the noise of the air jet far louder than that of the blower itself.
Thanks for the tip I will keep a look out for one, what power rating is yours? Could probably machine up a really small one on a brushless RC motor and mount it on the Z. Another project...Quote:
Originally Posted by Voicecoil
Mine's about 500W @ 50Hz mains, will do a bit more at 60Hz.Quote:
Originally Posted by devmonkey
Machine is going really well, I've made a few parts for the local flying club.
I'm now in need of a rotary axis, I have a couple of options:
1. Use the headstock and tail from an old rusty taig lathe I have with a belt drive off of a stepper or servo,
2. Convert a rotary table,
3. Buy one.
I need it quite quickly, can anyone recommend anything that is known to work, even if it is one of those chinese harmonic drives? I need something with a 100mm chuck and minimal backlash as it will be used for continuous processing not stop/lock.
I was looking at this, seems extremely cheap for a harmonic drive but they have them in europe so I could get it fast:
https://www.aliexpress.com/item/33025578546.html
Cheers, Joe
I needed an HTD5 pulley for a project, this was a bit odd as it needed to be fixed to a spinning bearing housing rather than to a shaft so I decided to make one on the machine. I used the cambam trochoidal plugin for the roughing allowing the entire part to be milled with a 3mm endmill, took a bit longer but meant no tool change. Part was cut dry with air to clear chips, worked out really well.
Attachment 28713 Attachment 28714
Trochoidal clearing is excellent, no gummy chips sticking to the endmill. This was cut from some 5000 series (not sure exact spec) scrap plate, it is quite gummy, would have been better in 6061 but I didn't have any to hand. Still the part is more than serviceable for its intended purpose which is to drive a multi-turn encoder (near zero load). Was cut at 3mm DOC, 15% stepover, 24k rpm, 3000mm/s for clearing (although the machine never gets anywhere near this on this part due to the tiny radius of the spirals).
https://youtu.be/skiw7pmDoQk
I will probably recut it with a high speed profile to finish, the finish pass was way too slow (600mm/s) which led to rubbing and the surface finish not being perfect. This was entirely my fault for rushing the CAM and not setting the feed.
Very nice. I happen to make two the other day for an encoder 28 tooth .
Attachment 28715
.
Attachment 28716
They are nice, what are they made out of and how did you cut that thread on the inside of the hollow one?Quote:
Originally Posted by Clive S
I just made it a baby brother, this one is going on an 8mm shaft with a 2mm shaft stuck in the end to go onto the encoder gearbox.
Attachment 28717 Attachment 28718 Attachment 28719
The thread was done on a Myford S7 converted to cnc with an encoder to do threading.
They are made out or 6082 I think
Didn't do a vid of the thread but had to make a male thread first. The hollow one is being fitted on the end of a spindle lathe to drive the encoder. The pin nut was off the lathe and used that for the fit 35x1.5mm
Attachment 28720
https://www.youtube.com/watch?v=MyLwFqa02Bc
https://www.youtube.com/watch?v=ZR_W3w_rews
https://www.youtube.com/watch?v=IiMME9BcBHw
'Great minds' and all that.
Yesterday I used the CamBam trochoidal pocket plugin to cut out the teeth for a ratchet made from Jarrah hardwood. Conventional shallow cuts tend to take the corners off the teeth where the grain is tangential to the wheel so being able to do a 12mm depth of cut with a 2mm diameter tool is a bonus. I still had to redraw the original ratchet design (produced in Gearotic which will also draw HTD and many other pulleys for you) with rounded teeth to avoid some chipping. This cut used a two-flute straight cutter with a speed of 1000mm/min and a stepover of 0.15 (0.3mm) and the maximum 24000 rpm. This took about 25 minutes for the 110mm diameter wheel.
Attachment 28721