Nice work
 

I must recognize that you inspire me a lot. Specially the way to fit one piece in other. Welding becomes a kid's play.
Here are a pic of my table:

Hey Marius

Correct, puzzle connections make it very easy to weld things up true and straight.. Your new table also looks good, looks a bit small though, are you downscaling from full size to smaller size?

Yes it's a small size 800x1600 working surface but is for small pieces and will have an indexer.

Very nice, I'm also looking into adding an indexer at some point, but it's still on the drawing table so to speak. :D

Did you modeled it before assembly? that size, maybe a little smaller, is what I have in mind, if you can share it it would be great. Very Nice too!!

Hi Kim,

I am slowly getting closer to starting a build and the more I look at this thread, the more convinced I become that linear bearing slides are the way to go.

I was wondering if you could tell us what size your used for each axis? SBR12 or 16, and maybe even 20 would seem to be too small for the X-axis, so I would guesstimate that you used either SBR25 or 30 for the X and Y, and 16 or 20 for the Z-slides.

In retrospect, given the performance of the machine, would you have gone larger, or smaller, with those slides? And why?

Also, three meter lengths of slides, if even available, are exceedingly expensive so most people just butt shorter lengths together. If you used this latter configuration, did you just simply butt them together or did you have the opposing ends precision bored (usually in a lathe) for dowel pins?

Cheers,

Brian
Taxachusetts

Regarding the linear bearings be sure to watch this very informative video.
It will help you see the needed precision for mounting rails and their use.

http://www.youtube.com/watch?v=rq4Pis6Zhf4

That was very interesting. The main take away message for me was the ability of the round rails to self-align. Given that our machines may not be perfectly flat straight and/or square (especially after welding), square rails may not be the better choice.

Thanx,

Brian

Hi Allehegny

The rails I used for my X axis is 20mm rails, and the y and z axis is only 16mm rails.. They are more than strong enough to hold the forces of the machine when in motion and when cutting. After I have fitted my gearboxes, my rack and pinions and my ballscrew, the performance of the machine it self have been significantly improved...
I have not yet had time to do some good quality testing yet, because of my new job, so I can't really tell you about the precision, but I expect it to be something around 0.1-0.3mm precision on all axis.. Which is more than enough for my needs.

The X-rails by the way is full length of 3meters, no butting here... :D

Hi Kim,
how about dust getting into the linear bush？ Linear bush are notorious with thier dust proofing characteristics as far as I know.

Ken

That problem should you be able to prevent by adding some good dust extraction to the machine. Right now I have none, so I dust off as much as I can. But so far so good, no dust in the bearings yet. There is a good scraber ring on the bearings, so dust do not actually enter the bearing. But still good dust extraction is always a good idea.

How about some tightly fitting rigid felt wipers on both faces of the bearing blocks?

I don't know exactly how you would do this for a CNC router, but in the machine tool world, the felt is cut to closely match the shape of the ways and a brass cover, of at least 16 gauge thickness and clearing the machine's ways (or, in this case, the linear bearing) by no more than 0.060", or a nominal 1/16", is also fabricated. Provision then is made to affix this sandwich to the block using a minimum of three machine screws. For machine tools, the felt would be further saturated with way oil, but that would attract and hold MDF dust and make for an interesting combination, to say the least - who knows, it might even work better. Furthermore, I'm not sure how the bearing blocks would tolerate the oil.

Rigid felt is available in sheets in several thicknesses and of varying stiffness from industrial supply houses. In the States, McMaster-Carr or MSC are good places to look.

Brian
Taxachusetts

I really dont think you need to be too concerned regarding dust ingress into linear bearings, if it was much of a problem the big iron manufacturers would have found a different solution, I cant recall a single big iron machine (SCM, Biesse, Weeke, Multicam etc etc) using anything else but linear bearings. I had a Biesse and an SCM working with copious amounts of MDF dust over a six year period (2x 8 hour shifts 5 days per week) without any negative effects - Note regular servicing and greasing was done (SCM had auto centralised greasing system - Biesse was manual)

Had a clog once, after oiling the wheels on Z axis in the same day I cut MDF and styrofoam.
Foam being driven by static charge flew onto wheels and slide, mixed with grease and finally cemented with fine mdf dust. I left out the cleaning after work that day, and in the morning it was so sticky, barely able to move.
So proper dust extraction, cleaning of guide ways and motion systems is essential. No way that unattended machine can work covered in dust.

Metal working machines have all the guides well hidden and lubricate them all the time automatically so they last a long time.

I wiped my machine down about once a week. A good liberal spraying of slicktop (table saw top) on my rails and rack kept everything slick and mostly clean. When cutting foam, it was a constant effort to hand vac the areas of the machine the standard dust collection.

I second the comments - no worries....just regular attention to keep it all working.

You can also buy double seals and scrapers in addition to the stock rubber seals.

Hi Kim
I also live in Denmark and we have already built a Mechmate in our workshop. However we built the rails in alluminum and now want to make them in steel. Did you buy your rails and can you share the contact? Or did you make them yourself and can you share the plans or your angle skate?

Hi Drew.

No secrets as to where I bought my linear rails.

www.slidesandballscrews.co.uk

Price was fair enough, and he delivered in full length to me. Me a bit carefull though, his packaging could be better, thank god for the materials ability to flex a bit when you mount it. :)

I'm a mad builder.
 

Sold the last one and am in the progress of building again.

Follow the thread here.
http://www.cnczone.com/forums/cnc_wo...x8_router.html

Here's a look at the present look. I bet one person inhere can see something familiar. :D

That looks very nice, I like it.

hi kim me also in the process of building something like yours

The main reason for the increased cost on my own design, is primarily weight and rigidity.

My machine weighs in at +1200kg and is so strong built that it will not have any chance of flexing what so ever.

Even my gantry weighs in at more than 180kg. The Gantry beam it self weighs a massive 90kg.

Nice looking machine Kim...

Although I don't think a MechMate for the same size weights much less at all. If I was to guess my machine is probably closer for 2000lbs.. Maybe I am completely wrong about the weight.

I did calculate the weight of my mechmate which was no more than around 6-700kg so I think there's a big difference in weight. My x axis beams weighs 180kg pr side which is the same weight as both the longitudal beams on the mechmate. Already there i'm up 180 kg on the mechmate. :)

But still 4-500 kg is a big difference in weight.

Kim, nice machine!
On your heavy machine, do you see real improvement over the cut quality over light duty MM?

The major difference I see is the ability to not have any chatter on circles of any kind, other things like errors are not as hazardouz on mine as on the MM. If I accidently make a plunge error, so the bit is too low, then I don't have to fear that the gantry comes of it's rollers or anything. In my initial setup of my Z axis, I accidently lost steps trying to peck drill with a endmill. When it wen't to the next hole it had lost enough steps so it was a bit over 1/2" into a 3/4 sheet of MDF when it suddenty pulled my 5mm endmill in the sheet at 12000mm/min, the only thing that moved a bit was the test sheet, the cut was actually allright and the endmill still lives to this day. :)

I have truly enjoyed reading your build, and you have a great machine well done!!

Just a quick question did you have to do any milling to any of the gantry on the ends where they join to the uprights from the rails in order to have a true gantry?

No I did not do any milling of the ends where they meet the uprights. Having things like that done here in Denmark, is quite costly...

I have shimmed the Z axis upon mounting it...

Please post some photos of your cut quality, especially curves to show chatter or lack of chatter.

There is next to no chatter at all in circles and such. But at very low speeds the bigger motors resonate a lot, so it might give a touch of chatter at low speeds, but I'll try and change the PSU and give them a little less power, right now they get 70V DC, so it's quite alot.. I'll try with 48V instead.

Kim,

You may have given us the main reason that we get excessive "chatter" when cutting curves.

All stepper motors have an area on their "speed curve" where they resonate. When I design process control computers that use stepper motors, I make sure that the motors ramp through that "resonating" space as quickly as possible so that the "process" can be accomplished.

On a CNC machine, one axis often has to move very slowly (primary resonating part of the speed curve). When you look at how a circle is cut, each line segment involves two axes. It's fairly easy to plot things out using a spreadsheet. You'll end up with four nearly identical segments of a circle. The only thing that changes in those four segments is which axis is master and which is slave (or which is dominant and which is recessive). Using a spreadsheet that only has sixteen line segments to make a very rough circle shows the interaction between the x and the y axis.

Anyway, back to resonance. If one axis is moving very slowly, it may actually NOT move when commanded. It may suddenly move several steps out of sequence as the motor resonates.

If you plot the circle being cut, you'll probably notice that the "chatter" occurs when one axis is barely moving.

The cure for the problem is to use motors that don't resonate (or motors that are perfectly controlled by the stepper driver to eliminate all resonance), or to use servo motors with expensive feedback systems.

Well, I did try to change the power to the stepper drives, it changed nothing. I can now probably only conclude that the stepper drives them selves are of poor quality.

The drives I have used is from Longs-motor in China, and they spoke highly of them, but it seems like they are just not of a good enough quality to be able to reduce chatter in my motors. So now I have opted for 2 Leadshine AM882 Drives for my X axis, hoping that this will help. Those drives can be programmed to reduce chatter in the motors, and they can be programmed via computer to give the best performance in an overall use. So croos your fingers, that I'm right about the drives. :)

Kim ever thought of EM508 from leadshine? don't they have them in stock yet? the Am882 are almost 141 US in India.

The EM508 can't take more than 50VDC, so it will not be usable. As the 48V PSU I have borrowed goes back, it was just to make a simple test to see if the PSU were the problem.

So I'm still gonna use the 70Vdc PSU, and the I'll just use the better AM882 from leadshine instead. I found them at around 300$US including shipping for the pair of them for the X axis here in Europe...

Kim,
Since x and y axes are used when cutting a circle, each one slows down and resonates at their own points on the circle, would you not need to upgrade both x and y to eliminate the chatter on the circle cuts?

Mike, here is a proposal for a definitive experiment:

Take a 200 pulse per rev stepper motor on a test bench,
with a large & accessible coupling driving to
a 2000 step/rev encoder

Drive motor with a 1/10th microstep drive. (In theory, 2000 steps into the drive will give one full turn and 2000 steps out of the encoder)
Use a variable frequency generator to get a steady stream of pulses into the drive (which will theoretically give smooth rotation of the motor)

Then, put in a "comparator" to see the difference between the input versus output pulse counts. Run at low speeds and with loading on the coupling. (I don't know how the comparator will work, but it should tell us if there is lag sometimes)

Would this make sense?

Yeah I would probably need to change the y axis drive also. But since the machine has been sold, then I will not put anymore money into it than nessecary.. :D And the Y axis does not sound as high as the x axis does... :)

Gerald,

You've made a good suggestion.

I have several "b" type motors (1/2" shaft extending out the back), but I don't have any 1/2" encoders. If I can find a good 1/2" encoder, I could hack things together. The front shaft could be coupled to a load to simulate actual operation.

As far as the comparator goes, that would just be a simple microcontroller that "clocks" whenever a pulse step is sensed and whenever an encoder pulse is sensed. Then, it would drive a simple two-digit LED display that showed the variation. For example, if the stepper pulsed, it would show a '1', if the encoder pulsed, it would subtract the '1' and show a '0'. That way, it would should how many pulses out of sync things were.

The variable speed pulse generator would just be an analog to digital signal converter in another microcontroller (like the Arduino Uno). Turning a "pot" would increase or decrease the speed. Software would shape the pulses to "square" them up.

It sounds like a good project for testing resonance. I'll see if I can find a good 1/2" encoder with 500 steps. The encoders are usually quadrature, so they output 4:1. A 500 'line' encoder would match a 2,000 step per revolution motor (driven with a 10:1 gecko driver).

From http://www.geckodrive.com/support/st...or-basics.html, there is this part:

Attachment 13329

It would be interesting to see how our typical Nema 34 motors behave themselves.

How can we help with such an experiment Mike?

Would we have to see the motors running on an oscope?