here's a better one; there's three switchable keyboard maps and macros too.
Attachment 4659
Printable View
here's a better one; there's three switchable keyboard maps and macros too.
Attachment 4659
Heres the link to the thread i was thinking of and the software you are looking for is called PYSTROMO
http://www.linuxcnc.org/component/op...3/lang,german/
Bookmarked! Thanks for that. Another subject to explore. :-)
Z axis question... I've read that minimising the distance from the spindle to the Y axis is a good thing to prevent flexing. Is that it or are there other reasons to do this??
What I suppose I'm asking is does getting it wrong affect the load that the spindle can handle or is there more to it?
thanks
Well it don't really minimise flex as so much as it doesn't waste cutting area.! But another, better reason IMO, to minimise offset is to help with balance and reduce un-even loadings on both Y and X Axis bearings.Quote:
Originally Posted by mocha
There are far more important areas on a Z axis that affect flex. . . Front Plate thickness and design combined with bearing/rail placement have far more impact than offset from Y axis.
A lot will depend on material and rail/bearing type in which is the best way to go about designing a Z axis with minimum flex.! . . . . You don't always have to use thick expensive material either and thinner material can be used with the right design.
Here's one that use's 9.5mm Ali and would be very strong.
Deleted...
[Duplicate post, not sure how I managed that given the time restraint]
Increasing that distance clearly increases the turning moment which results in the magnitude of the forces on the Y-axis bearings being greater. Also, for the same reason, if the Y axis ballnut is not directly between the Y-axis linear bearings then, for forces parallel to Y, you will get a lot of deflection as the parts in between don't have to flex much at all - it just 'rotates' about the ballnut since the ballnut is essentially the only support in that direction.Quote:
Originally Posted by mocha
Thanks chaps! Jazz, that's alloy porn! LOL, Very pretty. Is it in use / used or planned for the next one?
The location of the supported rails on their side is unusual isn't it? Most of the ones I've seen seem to be in the Z; up/down axis usually one facing up and one facing down. Any reason for doing it that way?
I've attached a few shots of something I was playing with to help me understand what I am trying to do... It's not to scale! more of a schematic block diagram sketch to see if it could be done, but comments are most welcome.
I've left out some of the elements so it can be seen easily. (like the colums parralell to the Z ballscrew joining the upper and lower Y axis motion, joining the upper and lower blue box sections etc.) and I've shown as bars things that could be plate etc. The purple areas are the supported rail, any other questions just shout. If you want to play with the Sketchup file PM me and I'll send it over as Google wont let me upload it, they must have standards! lol.
As I said it's not to scale and not an opimised design, putting the ball screw mount under the 3rd Y axis support, moving the Z ball screw closer to the spindle, etc. could all help to reduce the overall footprint - although the overall size should be spindle + ballnut + Y axis support? could drop it in the region of under 200mm??
I'm wondering if the ideal position for a high sided frame design be putting the whole of the Z axis UNDER the Y axis? (but I might have OD'd on the coffee this morning LOL)
Attachment 4675Attachment 4676Attachment 4677Attachment 4678Attachment 4679Attachment 4680Attachment 4681Attachment 4682
No not in use, Like a lot of stuff I do and make it was designed to make best use of cheap available materials, in this case the machine was going to be for a guy who had bought some really cheap 150x9.5mm Ali and was on a real tight budget.Quote:
Originally Posted by mocha
It actually never happened due him losing his job scraping the project, I ened up buying the Ali off him which luckly for him was is only outlay upto that date.
If you mean the Y axis rails then No they where just drawn that way, they could go either way round. The back plate and rail was just put there for affect really and this was just quick mock up drawing really not actually a finished design in any way. . . . . . Only posted to give some idea how thinner material could be used put still give a stiff Z axis.!!Quote:
Originally Posted by mocha
Regards your design I'm slightly struggling fully under stand the layout but my first initial reponse would be "WHY".??? . . . . Why all the complexity when you won't really gain any extra support over a conventional Z axis.
The way you have it drawn you are still relaying on just 2 rails/bearings and if the bit with rail on top thats jutting out from the Y axis with rails top n bot is not directly mounted to the gantry sides or X axis bearings plate then your in big trouble.!
If Z axis was supported on 4 sides with rails/bearings then yes I could see the bennifit but can't see any how you have it now. . Plus still the jutting out bit would need attention.
If you have the length and done right then the wide gantry with central Z axis (Ala Mech mate) can be very strong it just cost's MORE, more expense, more real estate, more work.! . . . trick is working out if it's worth that much MORE.:question:
So what you have there is a copy of the MECHMATE? that is the type of arrangement they use.
Attachment 4703Attachment 4704Attachment 4687
[edit: added pics 2 and 3, x axis in yellow! that might be clearer and make more sense!!]
Apologies for poor quality drawings!!!:redface:
Thanks Jazz!
Yes, the image probably doesn't make too much sense as it is, LOL, this might be clearer, although not necessarily better! :-)
In answer to your points;
Why? I'm thinking that the closer to the spindle that the supported rails of the Z are, the less leverage that can be applied to them, so the spindle mount is also the supported rail bearing mount.... This of course assumes that fitting the rails to the spindle is a good idea! lol
yep, ammended pic aboveQuote:
The way you have it drawn you are still relaying on just 2 rails/bearings and if the bit with rail on top thats jutting out from the Y axis with rails top n bot is not directly mounted to the gantry sides or X axis bearings plate then your in big trouble.!
Not familiar with that design, will go find it.Quote:
central Z axis (Ala Mech mate)
. .Quote:
...can be very strong it just cost's MORE, more expense, more real estate, more work.! .
Yep, the real estate is going to be my main issue on an 800 x 800 table,
Quote:
trick is working out if it's worth that much MORE.
LOL, and therein lies the answer! I'm guessing that if it was worth it, evolution would have saved it and it would have been done by now!
Interesting exercise in getting my head around some of the things that I've only read about so far.
Thanks, will go have a look at it!Quote:
Originally Posted by 2e0poz
:-)
Nope certainly wouldn't go with that layout.! . . . .Just think of all that weight levering on the Y & X axis bearings.? . . . Bad idea.:thumbdown:Quote:
Originally Posted by mocha
Go check the Mechmate out and you'll see how it could be done, thou it will make short work of your 800mm.!!
I can't pretend I understand the reasons, but I do agree with the conclusion! I'll stick with using a "traditional" Z axis if only because of time and cost restraints. :-)
Apart from the length of the Z ball screws, 400? 450?? I don't think I need to worry about the Z just yet. Still got other areas to sort in the next three weeks!
Mocha sorry didn't see this before but Doing it this way means the X axis is unsupported from under neath and could flex.?
I would still do it with this configuration but lift the whole thing up and sit it on the X axis bearings, basicly making a rectangle box section frame.
Like I say Spindel supported on four sides would be better but I see why you have done it this way to keep the width down, thou I think the extra strength would be worth the width loss.!
Mocha take a look at Rogers build, this is similar to what you want to do, he told me he would have taken a more traditional approach if he were to do it again.
http://www.mycncuk.com/forums/showth...-5-Years-in%21
there's some serious work gone into that! He mentions some sort of design flaw??
Ye I big design flaw.??. . . . He used springy unsupported round rail.!Quote:
Originally Posted by mocha
Putting one up and one down evens up the load ratings. Clearly the supported rail bearings are weaker in one direction as that portion of the bearing is 'missing'. Sure I've mentioned this before, but nevermind. I calculated it once by measuring the angular position of each of the rows of bearings in a SBR25 block and from that calculated the relative force rating. The figures I ened up with for the SBR25 blocks was 980N (from datasheet) and -340N (calculated). So clearly if both rails are the same way you get 1960N in one X direction and only 680N in the other, however if they are opposite it's 1320N for both up and down, and even for X directions.Quote:
Originally Posted by mocha
But... there's more to it than that. The round rails are connected to the aluminium support by a series of bolts into the rail from underneath. This connection isn't actually that strong (though clearly it's a whole lot better than nothing), so the rail will slill bend on the support with a force (if the beraings are mounted facing) parallel to X, or if the bearings are mounted on the same side they'll deflect with forces parallel to Z.
So it's debatable which is best...the force ratings above are a lot greater than what you will actually encounter, so perhaps deflection is more important because as the force increases the deflection will be greater. One day maybe I'll measure it.
Interesting that he used a worm drive...Quote:
Originally Posted by 2e0poz
This is similar to what was thinking of doing, and may still do, for my machine. The difference is I also considered having two ballscrews on Y:
http://www.mycncuk.com/forums/showth...h-X-and-Y-axis
Adding a third rail would help, but when the two rails are profile rails I don't think it will make much difference, as long as what the rails are mounted on is strong, as they are rated for an equal load in all directions.
No, I think he said something about it binding somewhere?? and having to "ease it" with a hammer (?I think...)
Although I don't intend to try it, I do still wonder if mounting the rails directly onto the spindle, parallel to the Y axis has any merit, especially if they were profiled rather than supported rail... file that one under mark 2 version ideas! :confused:
However, I've been working on the work area, (bed / table element) I wanted it to be adjustable to minimise the extension of the Z axis but still have the flexibility to accommadate different work heights.
The thought of driving the table up or down was discarded as too costly, handcranking, better but too complex, but I think I've found a way that might just work. Any comments welcome!
My work area, inside the frame, is something like 850 x 900. By making the bed bolt into place inside that frame, I get the bed as in the example on the left of the pic. Undo the 4 bolts, turn the bed other way up and rotate through 90 degrees and the bed is now 70mm higher, now supported by the box section on the other sides and locked back in place with the bolts again, now on a different side. By using a couple of 70mm box section "spacers" and longer bolts, I could get another 70mm too.
I'm not expecting to be changing heights every day... do those of you with some sort of adjustment on the bed height find that there is a sweet spot where it stays most of the time, or are you constantly fiddling with the height of the bed?
Attachment 4707
There's been no updates for a while as I've been assimilating Jonathans reading list! LOL. Thanks to everyone who has helped, guided, suggested and corrected my understanding. I've progressed from not knowing what I don't know to knowing enough to know I don't know enough!
The design is done, I've put the crayons away, the fiddling with it over and now it's time to get some parts to fill it! So with a little luck I'll come back in a couple of weeks with some goodies and get cracking with it. Next target will be getting the frame parts machined and assembled and the unit constucted by the end of November!
Cmon then lets see the doodle's.!!Quote:
Originally Posted by mocha
lol, I'm just heading out the door right now, but I'll try and upload something later! :-)
here's an early version of the frame! :heehee::heehee:
Attachment 4758
Attachment 4762doodle attached, front view.
well that was an interesting trip! lol, she seemed to think that wandering around markets looking for engineering bits did not form a constructive part of something called a "hol-i-day-to-geth-er"... what ever that is... didn't stop her raiding the fake handbag shop for all her friends though!
I only managed to bag some Kinco drivers before I was reeled in. I do get to go again on my own and I can meander through some of the most amazing product sellers I've ever seen. Imagine everything in the RS and farnell catalogs in a 9 storey building... and someone removed the index! lol, I spent a half day there and didn't get to see all of just one floor. I did see some other stuff there too, a big wall with a roof and a bigger wall on the top of a mountain and a house with 999 rooms... and about 2 miles between each of them. other than that, an amazing place, looking forward to going there again.
STILL awaiting my first delivery of bits, which are not due to arrive until the end of the month... :-(
I found a friend of a friend who fabricates for a living (and builds race cars in his spare time) and with some back scratching for a mutual 3rd friend he's agreed to look at the design from a fabbing point of view, the good news is that not only did he like what he saw, he's going to weld it for me, he can probably find me a good price for the metals too.
There's a couple of small changes he suggested to the way two of the corners are designed, in order to make it easier to weld up squarely, but otherwise it's looking good.
At the moment, I have one guy who will do the machining of the steel parts, another guy who will weld it all together, an assortment of advisors spread over 3 continents and a number of suppliers who are in the process of "supplying". One supplier who has let me down badly and one supplier who has been an absolute star and a number that are just dragging their small oriental feet!
LOL, This is turning into a international project management tutorial rather than a CNC build! :)
Quick update on this slow moving build!
The good news is that the parts aquired list is getting longer! but the bad news is that the 900+ revisions of this design is not going to make it work. :-( Building a scale model exposed a major problem in the assembly phase. Which probably explains why I'd not seen others of that type of design. So, onto the mark 5.5! Nothing too ambitious this time. Fixed gantry and rotating head with 6 linear actuators to move the bed.
<grin>
I'm shopping!
I'm shopped!
:-)