[yydoctt]

Hi guys,

For the past few years I've been considering building or buying a cnc machine for prototyping and building other machines. I'm somewhat addicted to reprap 3d printing!
Last week I saw the momus and knew it was the correct choice for me with a few modifications.


Ballscrews
The belts give the momus a great speed advantage but I'd like to mill aluminium motor mounts for printers and other machines. I am thinking 2010 screws are appropriate. (20mm diameter, 10mm lead). Are these chunky enough for 500mm of cutting? Fairly fast?

I notice there are a number of grades of accuracy and most use C7, what are the tolerances on these, what is the precision? I would want accuracy of about 0.05mm if possible.


Motors
I semi-understand the values but could someone help me with the importance of values? Low Impedance = high speed? But what current and voltage is appropriate? I guess I will use gekkos so what are others running with similar setups?


Spindle
I mentioned that I want to mill aluminium from time to time so have selected a Chinese 1.2kw water cooled VFD spindle, is this a good approach?

I have bought nothing and will complete the mechanical build before purchasing expensive parts so would appreciate advice until that point.

Thanks,
Tom

[OCNC]

Here's a link to a page on Bill Jesson's thread about his modified Momus build that uses screws instead of belts.

Also look at Sven's build thread for an alternate rail system as well as use of screws.

David's Build is also a screw modified build.

[louieatienza]

With steppers speed will come at the expense of resolution. While the drives can provide microsteeping, I don't know if it's someting I would rely upon. I think a C7 screw has a lead accuracy of about .002"/ft, which is about where you want to be.

For sizing steppers I'd recommend reading some of the articles on the GeckoDrive website. I feel a lot of people oversize their steppers, which can cause a lack of top end speed and power. Ballscrews are very efficient and it would take less power to drive the same weight as with an ACME screw.

As for spindles, realize that these spindles probably work best at higher RPMs, requiring higher feedrates to obtain a decent chipload. They probably don't have enough "oomph" to hog material at low RPM and deeper cut depth, as with a mill.

[yydoctt]

Here's a link to a page on Bill Jesson's thread about his modified Momus build that uses screws instead of belts.

Also look at Sven's build thread for an alternate rail system as well as use of screws.

David's Build is also a screw modified build.

Hi OCNC, thank you for your response. I've seen a lot of your posts in the Momus sub forum but couldn't find a build of your own?
I have read those posts paying particular attention to ger21's comments on bjessons's build about a poor combination of screw and motor, this is something I am trying to research to avoid now.

With steppers speed will come at the expense of resolution. While the drives can provide microsteeping, I don't know if it's someting I would rely upon. I think a C7 screw has a lead accuracy of about .002"/ft, which is about where you want to be.

For sizing steppers I'd recommend reading some of the articles on the GeckoDrive website. I feel a lot of people oversize their steppers, which can cause a lack of top end speed and power. Ballscrews are very efficient and it would take less power to drive the same weight as with an ACME screw.

As for spindles, realize that these spindles probably work best at higher RPMs, requiring higher feedrates to obtain a decent chipload. They probably don't have enough "oomph" to hog material at low RPM and deeper cut depth, as with a mill.

Louieatienza, that is some great advice and information, thanks!
Do you think a Ballscrews such as High precision ORIGINAL TAITAN TBI SFU 2010 ball screw for CNC machine-in Ball Screws from Industry & Business on Aliexpress.com would be appropriate? I can't find info on how many starts it has? The nuts don't mention backlash capabilities but will talk to the seller.

As for steppers, is microstepping not a standard for builds here? I use 1/16 on my printer with feedrates of 300mm/s over USB. I assume linuxcnc and a serial port can transmit data as quickly, even though this machine will have much lower feed?

The spindle seems to come standard on Chinese 3020 and 6040 machines. I assume it's more appropriate than a router? If not what else should I look at?

Thank you for the help guys!

[Devastator]

As for steppers, is microstepping not a standard for builds here?

Yes, but increasing microstepping beyond a certain point is a poor way to increase resolution. For instance, designing it for speed and then trying to get resolution by using 1/32 or higher is probably not the best way to do it. With certain higher microstep modes, your computer will be the bottleneck and the motors can't hold those fine microsteps reliably anyway. I can't use anything higher than 1/8 step on mine or the computer limits the feed to slower than I want to run it.

Design for the application. For instance if you are building a big machine for cutting plywood panels, go for speed. If you are building a small machine for PCB milling go for resolution. If you need to do both, build two machines.

[louieatienza]

With a machine the size of a Momus, you probably could use 2005 ballscrews. With the right steppers and drivers, you can get good speed and resolution. Microstepping also comes at a cost of decreased torque, though with drives such as GeckoDrives, they morph to full step at about 240rpm so you get the benefits of both. Of course if you use leadscrews too coarse, you may never see full stepping since the motor won't reach that morph speed.

I just built a small desktop machine, and with 200in-oz steppers and 48v PSU, I can achieve 275ipm rapids and have done test cuts at 200ipm. This is with 1-2"-8, 2 start (4tpi) leadscrews. I'm sure with a larger PSU and ballscrews I could get more speed, but I don't think it's necessary for such a small work envelope.

The G540 is locked at 10X microstepping, being based on the G250. The G251 I believe can do 1,2,5 and 10X microstepping. Leadshine has drives capable of over 100,000X microstepping. If I remember the history microstepping was invented to "smooth" out stepper movements at very slow speeds. They are not as linear as full step moves, though a lot depends on the driver and stepper quality.

[yydoctt]

Yes, but increasing microstepping beyond a certain point is a poor way to increase resolution. For instance, designing it for speed and then trying to get resolution by using 1/32 or higher is probably not the best way to do it. With certain higher microstep modes, your computer will be the bottleneck and the motors can't hold those fine microsteps reliably anyway. I can't use anything higher than 1/8 step on mine or the computer limits the feed to slower than I want to run it.

Design for the application. For instance if you are building a big machine for cutting plywood panels, go for speed. If you are building a small machine for PCB milling go for resolution. If you need to do both, build two machines.

Good points! Thanks for sharing. It makes sense to design for each application rather than multipurpose machining. Due to the frequency of using aluminium I will go for rigid and slow and grit my teeth or lower the microstepping during big wood jobs.

With a machine the size of a Momus, you probably could use 2005 ballscrews. With the right steppers and drivers, you can get good speed and resolution. Microstepping also comes at a cost of decreased torque, though with drives such as GeckoDrives, they morph to full step at about 240rpm so you get the benefits of both. Of course if you use leadscrews too coarse, you may never see full stepping since the motor won't reach that morph speed.

I just built a small desktop machine, and with 200in-oz steppers and 48v PSU, I can achieve 275ipm rapids and have done test cuts at 200ipm. This is with 1-2"-8, 2 start (4tpi) leadscrews. I'm sure with a larger PSU and ballscrews I could get more speed, but I don't think it's necessary for such a small work envelope.

The G540 is locked at 10X microstepping, being based on the G250. The G251 I believe can do 1,2,5 and 10X microstepping. Leadshine has drives capable of over 100,000X microstepping. If I remember the history microstepping was invented to "smooth" out stepper movements at very slow speeds. They are not as linear as full step moves, though a lot depends on the driver and stepper quality.

Thank you for the continued information! I think I will go for 2010 Ballscrews and see how it fairs. Ball screws require end machining and support bearings (from a thread in this forum) how does this differ from acme and why is it any more expensive than the acme mounts. I trust that I can DIY these mounts on a mill?

Motors and electronics is a very weak area for me, I will probably gauge it on common builds unless anybody has a good resource or advice for me and the setup described?

Please keep the advice coming, I need as much help as I can get!

Thanks,
Tom

[RicknBeachcrest]

Here is a great build thread that may give you some ideas.

http://www.cnczone.com/forums/cnc_wo...ear_rails.html

Rick

[yydoctt]

Here is a great build thread that may give you some ideas.

http://www.cnczone.com/forums/cnc_wo...ear_rails.html

Rick

Thank you Rick, I spent a good hour reading every post on that thread this morning! An extremely good and informative build. It makes me want to use rails to bolt together and make alignment easier...
I think the momus layout is more rigid with the raised gantry, so I will cost up an 8020 build of the momus using rails. I think although that thread displays good cutting of aluminium his build probably lacks a bit of stiffness which I hope to gain by adding steel supports, brackets and lengths everywhere.

I'm still unsure whether to use 2010 or 2005 ballscrews.. Luckily I can delay that decision for a few months whilst I make the mods to momus and build it.

[ger21]

Ball screws require end machining and support bearings (from a thread in this forum) how does this differ from acme and why is it any more expensive than the acme mounts.

If you want a comparable mounting system for acme and ballscrews, then you need to machine both of them.
People have come up with a cheap DIY method of mounting acme screws to save a considerable amount of money, as end machining and bearing blocks would typically cost many times more than the screws themselves. They do this be using 1/2" ID bearings and clamp on collars that slip over the outside diameter of the screws.
You could do the same with ballscrews, but it would be much bulkier, and quite a bit more money.
Personally, I machine the ends of my acme screws, as the mounting is much more compact.
Getting the ends machined from China adds very little to the cost. The support blocks and bearings are about $50-$60. Sue, you can make your own, but how much is your time worth? Here's a little info on making then.
5 Bears - Y axis ballscrew

I'm still unsure whether to use 2010 or 2005 ballscrews

On a small machine like that, 1605 or 1610 would be more than adequate, be cheaper, and give better acceleration due to the lower inertia. They have a 25% larger diameter than 1/2" acme.

Motors and electronics is a very weak area for me, I will probably gauge it on common builds unless anybody has a good resource or advice for me and the setup described?

You seem to be spending quite a bit of extra money on a spindle, and ballscrews. So just go ahead and get a G540 kit and 381oz motors from Automationtechnologies (Keling). It might cost $100-$200 more than the cheaper alternatives, but you'll have the best package available for your needs.

The G540 is locked at 10X microstepping, being based on the G250. The G251 I believe can do 1,2,5 and 10X microstepping.

No, the G250 and G251 are identical, except the G251 has screw terminals.

[yydoctt]

If you want a comparable mounting system for acme and ballscrews, then you need to machine both of them.
People have come up with a cheap DIY method of mounting acme screws to save a considerable amount of money, as end machining and bearing blocks would typically cost many times more than the screws themselves. They do this be using 1/2" ID bearings and clamp on collars that slip over the outside diameter of the screws.
You could do the same with ballscrews, but it would be much bulkier, and quite a bit more money.
Personally, I machine the ends of my acme screws, as the mounting is much more compact.
Getting the ends machined from China adds very little to the cost. The support blocks and bearings are about $50-$60. Sue, you can make your own, but how much is your time worth? Here's a little info on making then.
5 Bears - Y axis ballscrew

On a small machine like that, 1605 or 1610 would be more than adequate, be cheaper, and give better acceleration due to the lower inertia. They have a 25% larger diameter than 1/2" acme.

You seem to be spending quite a bit of extra money on a spindle, and ballscrews. So just go ahead and get a G540 kit and 381oz motors from Automationtechnologies (Keling). It might cost $100-$200 more than the cheaper alternatives, but you'll have the best package available for your needs.

No, the G250 and G251 are identical, except the G251 has screw terminals.

Thank you very much Ger21, that was the exact information and opinion I was looking to hear.
I saw the BK16 and BF16 also on the same site and was just a bit curious as to the cost being so cheap, whether they would be of any significant quality. I wouldn't want the mounts to be a weak area, just to save me some fabrication time.

Any testimonials for these Chinese mounts?

Thank you for your advice RE: ball screw size, I was going for stiffness and was concerned about 'whipping' that I read about recently. If these shouldn't concern me then I agree and would prefer to go with Dia.16mm.

I will definitely go with the Geckos, they have such high praise in this community!

[RicknBeachcrest]

I bought a set of Chinese mounts and found the quality level very poor. Luckily I purchased them from a US supplier who took them back. From my reading on the forum, Chinese mounts are hit and miss.

I ended up buying my ball screws and mounts from Misumi. Top notch; quality wise, but not cheap. I guess the good thing about taking your time building is that it gives you a some time to save up some cash between purchases of expensive components.

Misumi carries lots of stuff and their website is a little overwhelming at first
Here is a link to their economy fixed mount.
Support Units - Fixed Side, Economy, Square | Mechanical Components for Assembly Automation - Misumi eCatalog

This is the mount I used:
Support Units - Fixed Side, Square | Mechanical Components for Assembly Automation - Misumi eCatalog

Rick

[ger21]

From what I've read, on some of the BK blocks, the rubber seals rub and need to be trimmed a bit. There are a few threads that talk about it, and one has a lot of pics on doing it.

As for whipping, if you're under 30", it shouldn't be an issue, especially with the 1610's, which would be my choice.
I've never used any of the chinese screws or blocks. Just relaying what I've read.

[louieatienza]

Thank you for the continued information! I think I will go for 2010 Ballscrews and see how it fairs. Ball screws require end machining and support bearings (from a thread in this forum) how does this differ from acme and why is it any more expensive than the acme mounts. I trust that I can DIY these mounts on a mill?

Motors and electronics is a very weak area for me, I will probably gauge it on common builds unless anybody has a good resource or advice for me and the setup described?

Please keep the advice coming, I need as much help as I can get!

Thanks,
Tom

Tom,

On a lot of DIY builds with ACME screws, bearings with IDs same as the ACME screws are used in conjunction with shaft collars, and/or thrust bearings as an inexpensive solution. There is nothing that says this cannot be done with a ballscrew. However, unless you have access to CNC or at least a good mill to make the parts, it would be difficult to make them to the same accuracy as the ballscrew itself. In short, the bearing block may not be made to the same accuracy as the ballscrew, which would probably negate some of the benefit of using the ballscrew in the first place. For ACME screws in a DIY build, they seem to work just fine.

In fact if your cutting forces are not too high you could just use radial ball bearings with a slight preload. I bought a couple sets of dual radial bearing fixed end blocks from seller leifronchina on eBay and the quality was superior to lmb2008's, although it was more expensive. After screwing with Chai's blocks, opening the seals slightly with a burr, removing and cleaning the bearings, fiddling with different shims for the bearings, filing down the retaining nut because it was rubbing against the bearing plate... I think you get the point. I also purchased C5 accuracy bearing blocks from Marchant Dice, which were also of very high quality.

I have some pics here on one of my build threads: (see post 41 for the pics of the block comparisons)

http://www.cnczone.com/forums/diy-cn...router-10.html

I have a pic of the leifromchina block will look for it and post....

[yydoctt]

I bought a set of Chinese mounts and found the quality level very poor. Luckily I purchased them from a US supplier who took them back. From my reading on the forum, Chinese mounts are hit and miss.

I ended up buying my ball screws and mounts from Misumi. Top notch; quality wise, but not cheap. I guess the good thing about taking your time building is that it gives you a some time to save up some cash between purchases of expensive components.

Misumi carries lots of stuff and their website is a little overwhelming at first
Here is a link to their economy fixed mount.
Support Units - Fixed Side, Economy, Square | Mechanical Components for Assembly Automation - Misumi eCatalog

This is the mount I used:
Support Units - Fixed Side, Square | Mechanical Components for Assembly Automation - Misumi eCatalog

Rick

Thanks for the feedback, Rick. That makes it a tough call! I will have to find the relevant threads to see whether feedback is generally good or generally bad and let the seller know I wont accept poor quality. If I go down that route..

I presume the bad quality is with the fixed end and I can probably assume the floating end will be good in either situation?

From what I've read, on some of the BK blocks, the rubber seals rub and need to be trimmed a bit. There are a few threads that talk about it, and one has a lot of pics on doing it.

As for whipping, if you're under 30", it shouldn't be an issue, especially with the 1610's, which would be my choice.
I've never used any of the chinese screws or blocks. Just relaying what I've read.

Thanks Ger21, I will have to have a good search of the forums before committing to anything then...

Tom,

On a lot of DIY builds with ACME screws, bearings with IDs same as the ACME screws are used in conjunction with shaft collars, and/or thrust bearings as an inexpensive solution. There is nothing that says this cannot be done with a ballscrew. However, unless you have access to CNC or at least a good mill to make the parts, it would be difficult to make them to the same accuracy as the ballscrew itself. In short, the bearing block may not be made to the same accuracy as the ballscrew, which would probably negate some of the benefit of using the ballscrew in the first place. For ACME screws in a DIY build, they seem to work just fine.

In fact if your cutting forces are not too high you could just use radial ball bearings with a slight preload. I bought a couple sets of dual radial bearing fixed end blocks from seller leifronchina on eBay and the quality was superior to lmb2008's, although it was more expensive. After screwing with Chai's blocks, opening the seals slightly with a burr, removing and cleaning the bearings, fiddling with different shims for the bearings, filing down the retaining nut because it was rubbing against the bearing plate... I think you get the point. I also purchased C5 accuracy bearing blocks from Marchant Dice, which were also of very high quality.

I have some pics here on one of my build threads: (see post 41 for the pics of the block comparisons)

http://www.cnczone.com/forums/diy-cn...router-10.html

I have a pic of the leifromchina block will look for it and post....

Hi louieatienza, I'd appreciate that last photo if you can find it! Were the blocks from leifromchina good quality, c7 accuracy? Perhaps that is the way to go.

Thank you for the responses

[Walky]

Louie, do you know if leifromchina stocks varying quality blocks?, I was looking at their FK12 blocks and noticed they have them listed twice, at different prices (different quality?).

So far I've had success modifying every single block I've bought from Chai, but It'd be nice to have ready to run blocks which didn't need any work.

[louieatienza]

Walky, I don't know if Lei has different grades of blocks, you'll have to ask him I suppose. Here's a pic of his BK/BF blocks...