[pikolo]

Hello dear friends! I live in Europe and i can only find alluminium parts in metric...so is there anyone that has done the plans in metric?I searched the forum but couldnt find something specific ...what changes should be made to the plans so as to be able to build the cnc?Thanks alot in advance and sorry for my bad english..

[pikolo]

So after seeing no reply....i am trying to sketch it myself....it is hard i can say...the question that i have is this...The bearings are adjustable by 0.75 mm right? Also the gantry spacer does it have to be 3mm thickness?Or can it be 5 mm lets say?

[Mattlockhart]

Hi Pikolo, are you still working on this?
I think you are on the right track in sorting this out as understanding what each part does is important when you are trying to figure out where the dimensions can be altered a bit. For instance, as I see it, the gantry spacer was added to get proper spacing between the two bearings that sandwich the guide rail, without having to use a non standard sized piece for one of the others that are in the stack. I went through similar problems when I decided to expand the dimensions on my momus. Hard to vision when looking at the whole but break it down to the individual assemblies and how they relate to one another and it will become much clearer.

[pikolo]

Mattlockhart thanks for your reply!Yes in fact i am building it right now with many problems thogh finding the right materials....i changed the base by making it from 80x40x 1mm thick tube .The gantry is done and almost all the alluminium parts ....At start i could find cord rolled steel from a store but the guy selling them closed the store (probably retirement) and now i cant find the two of them tha are used for the side rails...I am trying to figure out what else can i use but i am facing the biggest problem of all to me...the material source.Also the delrin antibackshlash nut plus shipping tio Greece is very expensive and in addition the Mc master dont send to Greece and i had a hard time finding a similar rod!!At the time of speaking i have extended the x rail by 10to 20 mm(not sure but have made the base bigger just in case).Any thoughts?

[Mattlockhart]

Pikolo, I don't have any good ideas concerning replacing the cold rolled that doesn't entail a major rework of the parts. Here in North America cold rolled is fairly common. I would think it would be available (or maybe a suitable tool steel) somewhere in the E.U . Germany?? I do not think I would be tempted to substitute hot rolled steel. this has far too much mill scale and variation to be used for this purpose. While I was sourcing material for mine, I did a lot of searching and shipping / price comparison. Now, I am not in the designers head so I cannot say for sure but, I believe he used the cold rolled steel and skate bearings as a compromise between cost and accuracy. It works well for its intended purpose (cold rolled steel is dimensionally consistent for the tolerances required) and is reasonably inexpensive where it is readily available. Before I myself would consider using a more expensive steel with this design, I think I would consider using a round linear bearing system as is available on Ebay . this might even end up being close to the same cost ,(when shipping is figured in) with accuracy going up a bit. You would have to compare the cost implications and how much work this would entail to change over. There are many other options as well but this is one I may as yet change over to later.
I came across the shipping issue as well. Many US companies do not want to ship out of country to avoid legal issues with 'Strategic materials' Lead Screws may fall into this category. I did end up getting a lead screw and Delrin nut from a company called Roton out of the US. The price of shipping was almost twice the cost of the product. In hindsight I could have saved much money by driving all axes with lead screws just in the shipping costs alone. I have seen some lead screws in metric on Ebay coming out of Asia. This might be an option I would consider. I think a 12mm screw would probably work fine but you would have to drill your holes a little different to allow for the slightly larger diameter. Most vendors of lead screws also sell matching nuts. Since shipping costs are higher than the parts I would be tempted to purchase an additional nut or two or even an additional screw with a different pitch to try out.
I found the building of my machine to be a very enjoyable hobby in itself. I hope that you find the journey as pleasing as the final destination. let me know if can be of further assistance. Matt

[pikolo]

So my Friend Mattlockhart i have managed to find two crs bars but one cm shorter than in the momus cnc,...but thats ok i think...i also put the parts together nad my lead screw arrived from china today....BUT i dont have an antibackshlash nut or a threaded coupler...what i could find is a flexible aluminium coupler that i think wouldnt work in this situation and a bronze nut that came with the leadscrew...i really cant find an antibackshlash nut for this rod... 3D Printer 8mm Lead Screw Rod 300mm - 4 Start Z Axis 30cm Linear Rail Bar Shaft | eBay any thoughts?

[Mattlockhart]

I am using a flexible aluminum coupler I purchased off of ebay with good results so far. It is the type with a clamp in both sides and is unthreaded. The CRS bar being 1 cm short in length will not be a problem. Just adjust the mounting hole placement and you are good to go. The loss of 1 cm of travel is negligible. Unfortunately, I don't have a ready source for your anti backlash nut. Looks like your rod is a pretty common one so surely something is available in the metric world. These nuts are pretty basic and a quick Google search led me to several links and youtube video that have instructions in how to make your own (if further searches fail). a small piece of the rod you have could be made into a tap to facilitate this. Hope this is of help to you.

[pikolo]

Mattlockhart your idea was genius!So i made a tap from the lead screw and made a delrin nut....i was ready to cut it in two and the put a spring in it but i can see no backlash at all it is very good no play at all!So i am thinking why to put a spring cause it is already antibacklash? i will also submitting a video to see what i mean ....but please answer me is there any reason to put the spring if no backlash on the nut ?.

[Mattlockhart]

I am glad that information was helpful. I wish I could take credit for it but truly I believe I read about it somewhere.
I believe that I would go ahead and put the spring in it, if one was at hand. The nut is good right now because there is no wear on the nut. Once it its put into use it will slowly begin to loosen up and then the backlash will come into play. The addition of the spring makes this for the most part self adjusting so, it is pretty much future proofing your nut fitment for the wear that is someday bound to occur. Doing it now will mean you wont have to take the assembly apart sometime in the future. How long?? That I don't have enough experience to answer. Matt

[pikolo]

I finished the building procedure but please i need some more help...i am configuring mach 3 for working in mm....i have a leadscrew on z axis and it is a 4 start 2mm pitch so 8mm of movement per rotation..My motors are in 8x microsteping 1.8 angle and rated for 128 microsteps(i think this is the maximum) so in mach 3 i see the steps per... and with some calculations i see tha i should put 20,15748031 steps per so now for the motor to move the velocity mm per minute has become 11538 and the acceleration 1414,3921 also the step pulse is 4 and the dir pulse 0...is this correct or did i put very high the velocity and acceleration

[pikolo]

So i managed to find that the steps per unit are 31.94888178913738 for 50.08 mm in one revolution...i tried to cut a piece 50x50 mm and in the xaxis it cut 47.8 and in the y axis 49.5 so after that i tried to set it via mach3 steps per unit.....i did this and i tried again...the result was to cut almost perfect 50x50mm after thisitried to cut a longer piece 24.7 mm and in the x axis it was off 2 mm....i know that the pulleys i use are offcenteredm cause i opened the hole with a drill press is this the problem? please reply me if you have any ideas?