That’s a great development, Joe
Will we be able to select our colour ?
... methinks green would be worth a try.
MichaelG.
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That’s a great development, Joe
Will we be able to select our colour ?
... methinks green would be worth a try.
MichaelG.
An excellent idea, JohnQuote:
Originally Posted by John McNamara
Incidentally: More years ago than I care to remember, I did some environmental tests on a scanner for reading bar-codes at the supermarket check-out [the type that generates a criss-cross of lines] : The interesting thing about this one was that they had dispensed with most of the real hardware and optics ... They were spinning a hologram !!
I don’t know if it ever went into full production.
MichaelG.
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Edit: ... Just found supporting evidence: https://books.google.co.uk/books?id=...canner&f=false
This monochrome camera [with 2.2 micron pixels] may be of interest:
https://www.e-consystems.com/ar0521-...nir-camera.asp
MichaelG.
Work has been getting in the way of progressing my machine, but where I left off the laser system is working well enough to perform the operation (particularly with the raspberry pi version) however the process of position a jig and routing the steel frame into plane with a trim router was highly error prone.
1. It was difficult to level the jig since I didn't use concentric adjustment and clamping bolts,
2. The process requires that the laser doesn't move, the trim router height gauge doesn't move and the cutting tool doesn't break or chip throughout otherwise it has to be started over. Also the jig has to remain a planar plate and not wear, since I used tooling plate the surface got quite a lot of wear from the trim router.
This is what stopped me attempting it across the whole machine frame.
So I've had a bit of a rethink and come up with a different process that is hopefully a bit more forgiving and controlled. Rather than attempt to level the frame by grinding it the new processes will attempt to attach rail bearing sub plates to the frame such that these sub-plates are planar.
I'm thinking of using 10mm aluminium for the sub-plates. The plates would run the full length of the X axis on top of each steel beam and eventually the rails will be bolted to these plates. The plates will themselves be bolted to the steel frame in an adjustable manor such that they can be brought into plane using the laser, then they will be permanently fixed in place with a potting compound taking up the gap between plate and frame.
A few people have tried this using set screws to level the plates which seems quite fiddly unless you go the trouble of making concentric adjustment/locking bolts.
What I'm proposing is to take each plate and drill two sets of holes along the centre line. The first set will be counterbored and used to bolt the plate down to the steel frame, the second set will be used to inject the potting compound. To allow the plates to float above the frame but also be held accurately in height by the bolts I'm thinking a compressible gasket could be run down each side of the plate. As the bolts are tightened the gasket would compress pushing the plate up hard against the bolt, this is simpler than grub screws and locking bolts.
To prevent the two plates (one for each X rail) tilting they would be coupled together with lengths of angle during the process.
The laser would be setup and both plates adjusted into plane using the bolts, once everything is level potting compound would be injected through the remaining holes. The compressed gasket will now act to contain the potting compound.
I think this has a number of advantages,
1. The entire leveling process can be completed before making a permanent adjustment to the machine,
2. I would be directly leveling the final machine surface (the sub-plate) rather than some tool that is then used to machine the frame.
I have sketched this up, would welcome thoughts on it.
Attachment 27431
Hi devmonkey,Quote:
Originally Posted by devmonkey
I think you might need 2 rows of bolts rather then the 1 row in the middle.
This will allow for correction of axial deviations.
Did you calculate the expected flex of the plate in relation to the gasket compression forces? This would dictate the number of bolts in relation to the maximum expected compression.
As said before all thing look like made out of gummy now we can measure things in microns.
I might be able to start measuring my machine tomorrow unless shmbo thinks of something more important.
Grtz Bert.
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Quote:
Originally Posted by driftspin
Hi Bert,
I was hoping that bolting the two sub-plates together with angle would go a large way to reducing the axial deviation (twist), but we'll have to see.
I will calculate the compression forces required after measuring various gasket materials by squashing them with a known mass. If I start with plate that is relatively flat then most of the adjustment will be bringing these two flats into plane, not so much will be bending the plates into plane which requires significantly more force from the gasket. It maybe that a combination of gasket and hard shims under plate bends is required.
Will go hunting for some 10mm aluminium tomorrow and some gasket materials.
Cheers, Joe
Hi Joe (Devmonkey)
Hi All
Firstly I am assuming profiled rails are being used not round rail for high accuracy, repeatability and negligible backlash.
Lateral adjustment of rails is difficult, particularly when you take into account the small amount of adjustment allowed by the clearance around the mounting screw in the bored hole in the linear rails. for type 25 rails typically a 6mm hole and a 5mm machine screw. This only allows +- 0.5 mm of lateral adjustment, and this is if all the mounting holes are perfectly placed. Note in the description the order of processing to minimise chips creeping into the joining surface and lifting the rail.
To solve this problem I devised method where the rails were positioned laterally first using cams. Once this was done I drilled and tapped the mounting holes using an inexpensively built jig. You can make the cams yourself or get them laser cut. You still have to countersink them as detailed in the link.
It is documented here:
https://www.model-engineer.co.uk/for....asp?th=139042
The method worked very well. Alas I have not completed the machine.
I can't wait to get back to it! Alas work has been getting in my way too.
Regards
John
I managed to buy a monochrome webcam years ago, it was expensive over £200 and I had to buy it from China has highly specialised.Quote:
Originally Posted by devmonkey
It only saw Far Red (Near Infrared) specifically to see phytochrome reactions in plants.
I found a few different self adhesive glazing gaskets to experiment with. The one that works best is a 5x10mm rectangular profile neoprene strip, no idea where it came from. It isn't the very soft foam draft stop stuff, nor is it full rubber, it is designed to be compressed between the rebate and the glass on a fixed window. It is a closed cell structure not the sponge.
I also picked up the aluminium from SPA, huge stocks and fantastic price with cash at the door, perfectly happy with me picking up a couple of lengths.
So the experiment was to check the compression rate of the gasket and also whether I could inject some potting compound. I used around 400mm of 50x6 flat bar and clamped it into two lengths of the gasket stuck to a bit of 4x2. With the clamps at maximum pressure the gasket was compressed to about 2mm, the clamping force from the bolts I'm planning to use will be at least as much as from these hand clamps. Also the gasket is strong enough to just distort the aluminium which is perfect.
A 6mm hole was drilled in the middle for injection and countersunk. I used a normal decorators caulk gun to inject glazing sealant which has about the same consistency as West's 105/205 colloidal silica thickened epoxy which is what I will use on the actual job. The gun was pressed hard against the countersunk hole and sealant injected. I had to use quite a lot of force but it pushed the sealant through easily,.
So not very scientific but all very promising. Next step is to drill up the sub-plates and get them mounted on the machine frame.
Attachment 27436 Attachment 27437 Attachment 27438
Ok so i found a little time to do a leveling test at the new home of the machine.
I have setup the laser pointing along the long axis crosshair at about the middle of the gantry.
My flexing concrete floor is making things much harder then i expected while measuring adjusting and measuring again.
Walking around influences measurements.
My concrete floor is cast on sand, dont have any more information about it now.
In general all 4 x,y corners are in the same plane now .. within about 5 um.
Trying to get it any better seems silly compared to what walking around does to the measurements.
In the end my goal is checking the machine for general flatness and setting it up level
Both the long axis now look like they are within 10um deviation over 1800 mm of travel, this is far better than i expected.
Thank you epoxy.
Having the laser setup on a solid object other than the cnc table frame is a must.
When connected to the frame things get complicated quickly when 1 corner is adjusted everything changes.
Like mentioned here before, now we can visualize micrometers everything looks like made of jelly.
The gantry though looks like it has a deviation of about 50 um upward in the middle. This is a bit weird to me, the epoxy proces was done the same way and the axis is much shorter. There was no welding after epoxy.
I am going to re test this axis by moving the laser 90deg and in line with the gantry.
This should cancel out some optics quality issues. I guess the projected line could be non straight.
Thank you guys, for this cool solution.
Grtz Bert.
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