[Biff]

This is my first machine and my first design. Maybe not smart to do it all on the first go but something I wanted to do.

So the plan is a fixed gantry desktop setup. Working envelope is 12" x 18" x 4". I don't have any plans really to do anything over a sheet of wood thick but I probably will in the future so I just picked 4" in the Z out of thin air - any suggestions otherwise? Will primarily be working with wood though I'll likely mill a PCB at some point. I'd also like to be able to do some light aluminum work, as in cut some parts out of 1/4" sheet.

What I've come up with so far is to get a complete drive/linear motion kit off the bay with SBR20 linear bearings and 1610 ball screws. I already have an electronics kit from Keling wth 3x 381oz-in steppers and g540 driver and power supply (48V IIRC). The main frame and gantry up-rights are 1545 profile 80/20 with the frame having 1530 cross pieces to mount the rails on. The gantry cross piece is 3060 and there is a piece of 1/4" x 6" steel plate on the front of that to make mounting the Y axis rails easier. Plates for Z axis and router mounting plate are 3/8" aluminum. FWIW that is a bosch colt drawn on it now (I already have one) though I might opt for a slightly larger unit.

Sorry no fancy renderings and the colours are arbitrarily chosen just for contrast. I haven't drawn in much of the finer details yet like stepper motor mounting plates, limit switches, etc. as I wanted to get some input on how I'm doing so far. I'll also change the router mount to something that helps stiffen the plate that it's mounted on as well. One concern I have is I haven't figured out how I'm going to attach the gantry up-rights to the frame and it looks like a weak point to me. Ideas?

Thanks for any help,
Ryan

[awerby]

It looks like a fairly standard fixed bridge/moving table design. You don't really need to use 80-20 extrusions, since the frame and bridge don't move - that all can be as heavy as it wants to be, and more mass is usually better. The G540 is a good choice, but the SBR rails aren't as good as square-profile rails. In the sizes you need them, they shouldn't be too expensive on ebay or wherever. Using aluminum on your Z-axis is a good idea, since that's the only one where the weight works against you. Make sure the ball screws you use have enough precision for your applications; the cheapest ones aren't intended for leadscrews, and you'd be better off with acme screws made to higher standards. They'll also be more resistant to backdriving and dropping the spindle when the power's turned off. The G540 has 4 drivers, so if you're not planning a 4th axis you might consider using two motors, one on each side but slaved together to drive the table, instead of one in the middle.

[handlewanker]

Hi.....on the subject of ballscrews, what parameters do you look for on EBAY when the title just says 1605 ball screw.... or anti backlash ball screw..... or single ball screw.nut.......they all have the same design of a single ball nut which will eventually go slack and have backlash as they are similar in construction to using single deep groove radial ball races in a thrust configuration, and in that mode will soon exhibit backlash unless two radial bearings are used like you would with angular contacts.

Having two ballnuts in line would enable you to back one against the other to take up the slack.

I see also a double ballnut in a complete package, IE, two nuts in one..... probably with some spring loading to keep the nuts apart and exert axial pre load to eliminate any backlash from wear.

But there is no actual stated difference for ball screws as regards to precision, except that the cheapest ones are not machined on the ends and come as a plain length of ball screw rod with a nut.....user to machine to requirements.

Does the precision part refer to rolled as opposed to ground screws.......non of the EBAY screws state this specification (non that I could find).

So.....what do we look for in a ball screw as regards to X and y axis movements where distance for pitching and machined dimensions are important?

I also have a fixed gantry router on the drawing board and have now gone to a model mock up to check the overall build layout etc.

It's only a modest 250mmX200mm table travel with 100mm in the Z as I only need/want to do small stuff and this is what dictates the build pattern.

Without hijacking this thread, what do we look for when sourcing ball screws on EBAY?

There is bags of room under the table to fit a double ball nut that will keep backlash as non existent, so as the nut and the screw are two different entities....where does the precision come in, as in what description do we/I look for?

BTW, I don't think a double screw drive for the table is necessary in a moving table router.....it definitely is with a moving gantry type of router.
Ian.

[cyclestart]

One concern I have is I haven't figured out how I'm going to attach the gantry up-rights to the frame and it looks like a weak point to me. Ideas?

Bolting the uprights to the sides of the box frame rather than the top ? Might be difficult if you use extrusions (?), I have no experience with the 80/20 style stuff.

[wizard]

This is my first machine and my first design. Maybe not smart to do it all on the first go but something I wanted to do.

Good enough reason right there.

So the plan is a fixed gantry desktop setup. Working envelope is 12" x 18" x 4". I don't have any plans really to do anything over a sheet of wood thick but I probably will in the future so I just picked 4" in the Z out of thin air - any suggestions otherwise? Will primarily be working with wood though I'll likely mill a PCB at some point. I'd also like to be able to do some light aluminum work, as in cut some parts out of 1/4" sheet.

The size seems about right for PCB work. The more Z you add the more leverage you have when it comes to twisting things, that being said 4" isn't bad for a PCB machine. It could be a problem for wood working though. It depends upon what you intend to do with the machine, but you need to consider the spoil board, work piece thickness, retention/clamping and make sure you have the required tool clearance. It would be easy to use up 3-1/2" of space just setting up to do sheet goods.

What I've come up with so far is to get a complete drive/linear motion kit off the bay with SBR20 linear bearings and 1610 ball screws. I already have an electronics kit from Keling wth 3x 381oz-in steppers and g540 driver and power supply (48V IIRC). The main frame and gantry up-rights are 1545 profile 80/20 with the frame having 1530 cross pieces to mount the rails on. The gantry cross piece is 3060 and there is a piece of 1/4" x 6" steel plate on the front of that to make mounting the Y axis rails easier. Plates for Z axis and router mounting plate are 3/8" aluminum. FWIW that is a bosch colt drawn on it now (I already have one) though I might opt for a slightly larger unit.

Just a bit of warning, apparently the QC on the Colt has gone down hill and buyers are often finding terrible runout. Doing PCB work requires fairly high performance out of a PCB mill if you are targeting modern surface mount components as such I'm not sure I'd go with imported SBR20's. You really want a precise fit so the quality of components will matter.

For the bed especially you may want the table riding on profile rails. Further you will want a stiff frame that you can have machined to produce absolutely flat and parallel mounting surfaces for the profile rails. 80/20 simply isn't beefy enough to be machined flat in my mind and for PCB work you really need to keep the relationship between axis constant parallel and square.

By the way yes there are electronic ways to map and keep the cutter level to the PCB. In fact it is needed due to variability in the thickness of the raw material. I just believe it makes life easier to start out with a precisely built machine here.

Sorry no fancy renderings and the colours are arbitrarily chosen just for contrast. I haven't drawn in much of the finer details yet like stepper motor mounting plates, limit switches, etc. as I wanted to get some input on how I'm doing so far. I'll also change the router mount to something that helps stiffen the plate that it's mounted on as well. One concern I have is I haven't figured out how I'm going to attach the gantry up-rights to the frame and it looks like a weak point to me. Ideas?

It doesn't look too bad right now for a first go around. As someone else mentioned you don't need to to go the 80/20 route for the gantry and like. Mass and stiffness do make a difference also I'm not sure how you will be fastening your uprights to the machine base but you don't want to make that a weak point.

Thanks for any help,
Ryan

Everyone has different requirements or demands for their machine. When you mentioned PCB work that can imply a range of precision requirements. Due to that I suggested above to build to a higher level of quality than a machine focused on woodworking. Even then it depends upon your goals, but if you want to do things like route traces between surface mount pads then I think a focus on a more precise build is worth the effort. This means for the most case zero slop and backlash because otherwise your cutting forces aren't that great. In also means flat and parallel axis that are otherwise aligned properly.

The flip side here is that 80/20 or similar extrusions are easy to work with in a home shop. A welded up frame may require you to employ the services of a welder and machine shop or just a machine shop depending upon your access to tooling and your shop. However for small frames the costs here shouldn't be massive. That is you should be able to set the frame on most mills without too much effort.

[SteveWill]

I would move the clamps on the router apart more.

[handlewanker]

Hi, I always get the feeling when extrusions are mentioned, especially in frame work, that the user does not have a lot of engineering basic skills, as in working with metal for an occupation as opposed to just hobbying, hence the "meccano" construction of extrusions which in itself opens a whole can of worms due to the compromise that must be when pre formed sections must mate at right angles with other preformed sections......no room for flexibility in the design.

Looking at the drawings in post #1 I get the impression that if this were translated into solid plate metal with aluminium of decent thickness instead of hollow extrusion material and so allowing for sections to be drilled and tapped and solidly bolted to each other, then it would make the construction 100% easier to achieve, while at the same time imbuing it with strength and rigidity and a degree of mass.

There's a good reason the Chinese router imports all use solid aluminium construction for the main gantry upright frames (even if they are all mainly a moving gantry type) with the lower framework formed from extrusions, mainly for economy......the uprights need to have more body in the longitudinal direction (width) coupled with adequate thickness to resist sideways deflection which you can't achieve with a preformed extrusion.

There are two main forces at play here........a left to right deflection from the cutter acting against the main uprights and another twisting effect to the crossbeam also from the cutter forces.

It doesn't matter how high you make the Z axis clearance beneath the crossbeam to clear a high profile job as the same cutter forces will still act on the beam, but it is significant when the job is low on the table and the beam is high above it so giving a long lever effect.

This can be prevented by mounting the job on a platform to bring it up nearer the bottom of the beam and so reducing the leverage exerted.

By this I mean that if the Z axis has a small travel and the clearance beneath the beam is large, you will need to bring the job up to allow the Z axis to do it's work, even if the Z axis doesn't come all the way down to the table surface.

You can still create printed circuit boards 100mm up off the table if they are mounted on a raised platform, and this will allow you to also work on jobs that normally would not pass under the gantry crossbeam if it was too low..

I would think that with a 3020 type router and a 100mm clearance under the beam, the ability to work on a block 100 mm thick would be a big advantage even if you could not go all the way from top to bottom of the block with the cutter.

It just depends on if you anticipate only doing low profile work and never need to have anything higher than 40 or 50mm which cuts out having any work held in a fixture or vice etc, and makes drilling anything difficult when you need to get the Z axis high enough to clear the drill bits.

So, for the gantry sides, I would suggest it can be higher, but it must be thicker in section and wider at the base.

Being a moving table means you can have the gantry sides angled down to a wide base and continue along the sides of the frame to the end.....this will add strength to the ability of the crossbeam to resist fore and aft deflection.
Ian.

[G59]

a single ball nut which will eventually go slack and have backlash

B.S. Stop telling everybody that Handle. A good quality NSK single nut ballscrew can be '0' Backlash and last for years with the same tolerance. I own an old Tree mill, used 6+ hours a day, with single nut NSK (2805) ballscrew, with 34+yrs on the Z Axis. measurable backlash is 0.00015. Stop feeding people your B.S.
Look at most new machines out there. They still use single nut ballscrews. The nut, balls, and screw are all at play when it comes to backlash. Furthermore, rarely will you get absolute '0' backlash even with double nuts and all the preload you can put in it. Their is always going to be some backlash either created by the screw stretch or compression, or your end bearings will give not to mention all the support assembly to keep everything running smoothly and your couplings etc.......
If you want to help people, advise them that a double nut will take twice the room under the carriage reducing your overall Axis travel and that the price will also double. Tell them also that they are not adjustable and they too will wear out and at a greater rate then a single ball assembly due to the increased friction imposed by the preload of the second nut. Tell them there is also the possibility that stronger motors may be required as the increased rotational resistance is noticeably greater then a single ball assembly. After all that, then tell them why you don't have any in your machine.
Their is too much B.S. being fed to the hobbyist it's almost unbearable.
Be smart everyone. Always look at what manufacturers are doing to their machines and ask why they did some things a certain way. Look before you come here and get ill advised by thread lurkers that pray on your inexperience.

For 'real world info' here is a link.
Ball-screw basics: Debunking the myths | Mechanical Drives content from Machine Design

[handlewanker]

Huh.....I expect not everybody buys the very best ball screws, certainly not the average DIYér who sources his materials on EBAY etc, and rolled ball screws are not the very best but adequate for the need.

Your comparison of a commercial Tree mill to a DIY aluminium built router is like brass buttons on a Rolls Royce, totally out of wack.....be real, come down off your platform and see what the real DIY brigade is investing in.

Suggesting that forces that "could" stretch or compress a ball screw exist in a DIY router is bordering on the ludicrous.

True, you can get backlash movement from flexing at the attachment points of the ball screw mounting end brackets, but that is frame design not ball screw failure, and no amount of double ball nuts will cure that problem.

As I stated, a ball screw is like a deep groove radial ball race, except it works on a spiral and so gives axial movement.....but the aspect of the ball in the groove still applies to both components.......the difference is that a deep groove radial bearing is designed to carry radial forces not axial, and if you consider the design of the ball screw it is in the same mode.......it is applying axial forces to the flanks of the ball groove on the screw.

If you apply axial forces to a deep groove radial bearing it will soon fail to be useable as a radial bearing and have axial slop......this will also affect the ball screw and you get backlash eventually hence the need for double ball nuts similar to having two nuts on an acme threads to take up the wear in the nut.

All very interesting no doubt, but the average DIY constructor would not notice some backlash in his economical ball screw after a year of on off usage, so my suggesting double ball nuts is purely as a matter of interest.

In the design of a router with a moving table the rails are under the table and move with it, and the bearing blocks are attached to the base plate.

Due to the need to have some load carrying stability the bearing blocks need to be axially spaced a part form one another which means the table is longer than the actual work area.....the rails cannot move out of the bearing blocks at each end of their travel.

Therefore there is quite a bit of room axially to have two ball nuts fitted to the ball screw and tensioned apart to give an anti backlash component to even the cheapest ball screw, and one extra 1605 ball nut is quite cheap.

I would suggest having two ball nuts for the screw driving the table as this is where most of the movement occurs especially rapids which tend to eat at cheap ball screw case hardenings.

The design I'm working on will have two 12mm SBR linear rails per side under the table and two ball nuts for the singe centrally mounted 15mm X 5mm pitch ball screw.
Ian.

[gio666]

For the bed especially you may want the table riding on profile rails. Further you will want a stiff frame that you can have machined to produce absolutely flat and parallel mounting surfaces for the profile rails. 80/20 simply isn't beefy enough to be machined flat in my mind and for PCB work you really need to keep the relationship between axis constant parallel and square.

.

You must be joking,

[gio666]

Huh.....I expect not everybody buys the very best ball screws, certainly not the average DIYér who sources his materials on EBAY etc, and rolled ball screws are not the very best but adequate for the need.

Ian.

There lots of good rolled ballscrews. I have yet to see problem with Taiwan rolled screws. 95% of machines made and almost all home machines would gain nothing using ground ballscrews. I have yet to see a ballscrew that has worn out

[gio666]

As I stated, a ball screw is like a deep groove radial ball race, except it works on a spiral and so gives axial movement.....but the aspect of the ball in the groove still applies to both components.......the difference is that a deep groove radial bearing is designed to carry radial forces not axial, and if you consider the design of the ball screw it is in the same mode.......it is applying axial forces to the flanks of the ball groove on the screw.


Ian.

Ballscrews take axial load, if it didn't take axial load you would get backlash .

[gio666]

If you apply axial forces to a deep groove radial bearing it will soon fail to be useable as a radial bearing and have axial slop......this will also affect the ball screw and you get backlash eventually hence the need for double ball nuts similar to having two nuts on an acme threads to take up the wear in the nut.

All very interesting no doubt, but the average DIY constructor would not notice some backlash in his economical ball screw after a year of on off usage, so my suggesting double ball nuts is purely as a matter of interest.


Ian.

For ballscrews you would not use single row deep groove bearings like the 6000 series

You use double row angular contact bearings, like 3000 or 5000 series, they will not wear out, if you dont use proper stuff of course stuff will fail .
If you even have more massive axial load , you use face to face 7000 series

[gio666]

Hi, I always get the feeling when extrusions are mentioned, especially in frame work, that the user does not have a lot of engineering basic skills, as in working with metal for an occupation as opposed to just hobbying, hence the "meccano" construction of extrusions which in itself opens a whole can of worms due to the compromise that must be when pre formed sections must mate at right angles with other preformed sections......no room for flexibility in the design.


Ian.

Do you have paper for engineering ? how many machines have you made, I have sold 100s and 100s of machines with aluminum profiles, Machines very accurate and extremely strong

XZero CNC Routers

[joeybagadonuts]

There lots of good rolled ballscrews. I have yet to see problem with Taiwan rolled screws. 95% of machines made and almost all home machines would gain nothing using ground ballscrews. I have yet to see a ballscrew that has worn out

George,

So tell me how the ballscrew on my pretzel maker got like this?
Live from Downtown Burbank, home of the super deluxe jelly roll.

Joey B

[gio666]

George,

So tell me how the ballscrew on my pretzel maker got like this?
Live from Downtown Burbank, home of the super deluxe jelly roll.

Joey B

Must be from china lol must also be big jelly rolls or from just deep groove bearing

[handlewanker]

For ballscrews you would not use single row deep groove bearings like the 6000 series

You use double row angular contact bearings, like 3000 or 5000 series, they will not wear out, if you dont use proper stuff of course stuff will fail .
If you even have more massive axial load , you use face to face 7000 series

Hi, there is some confusion here.......I was comparing the design of a ball screw to a deep row radial bearing, not for the bearings that you must have at either end of the ball screw mounting.

Unless you have a double ball nut (or two single ball nuts in line) you will eventually get backlash as there is nothing in the single nut to compensate for wear.

This effect is the same when you use a deep row ball race and subject it to end thrust loading........you CAN use two deep row radial balraces in the same manner as angular contact bearings for thrust applications if you provide some end play adjustment.....for which they are not designed to cater for but will work after a fashion......angular contact bearings work better in this mode.

So, if you have two single ball nuts on a ballscrew you can, like two angular contact ball races, tension them against one another to take up the slack or pre-load them to eliminate backlash.

Tell me you can't and the reason why.
Ian.

[G59]

So tell me how the ballscrew on my pretzel maker got like this?

Ummmmmmmm...................................Photos hop.......................LOL.

No, but seriously, rolled ballscrews have their place and their accuracy is 10 folds compared to the first ones made years ago. Yes Ballscrews work on the principal of axial forces. A set of Angular contact bearings at one end, give the necessary preload. 80/20 profile certainly can be used to make an accurate machine, but you must realize and stay within it's limit, in which most DIY and some general routers, do.

I'm not just picking on handlewanker, I see these engineering experts all the time giving their hypothetical theories on this forum, steering people in the wrong direction. That just burns me up. It's sad to see that many refuse to inform themselves by doing their own research first, before posting on these types of forums . Sure they come here for help, but the amount of real technical help out there is available and is enormous in comparison to a couple decades ago.
When I see a thread like this, I always think to give the OP a true and accurate response that is based on my 25 yrs of experience as an engineer.

Engineering is my life.

Also saying that I'm out to lunch with stretch and compression on the screw? Yes, he's right in the case of a router, but it most certainly does exist in heavy and large machines .

I'm still waiting to see his machine as for nearly two years he has been saying, he is building an ultimate machine that will surpass many of the DIY's, expectations. And who am I to judge, he may very well know something that I don't.

Show us a 3D rendering or a simple drawing. I want to learn too.

BTW, Those cheap Chinese ballscrews are popular in the RErap bunch as they are super cheap to get linear motion.
I think most of the router crowd are more into professional and repeatable results. Many have put machines together and actually make a living out of it.

For the original poster,(OP), try and make it as accurate as you can with what you can afford. Ballscrews can get super expensive and very quickly at that. If it was my build, things like ball screws retain their value well even when used. So invest a little now and save yourself a headache later. Have a look at Misumi's website. Tons of info there and even videos if your into that. They also carry most of the parts you'll need.

And one more thing, when shopping eBay, pay attention to the price but especially the shipping. Many sellers like to tack on an outrageous cost to shipping so they can ensure they make a profit, and usually by using this unfair practice.

Take care.

[handlewanker]

Hi G59, you may be a gifted engineer and well able to appreciate the need for heavy machine practice where light componentry would not cut the muster, but as the poster of this thread is dealing with intended very small work loads and also a very small machine too, going overboard on the ball screw aspect is totally.....a misconception.

I quote a price for a 400mm long 1605 ballscrew and nut on EBAY.....the screw being unmachined at each end.....$39 post free........if you go to the screw with ends machined you would pay $79 post free.

BTW.......where did you ever get the idea that I have been working on the design and build for an ultimate "machine" for the last 2 years.......2 weeks at the most, and it has now gone from design concept to model.....not wanting to hijack the thread any further, I'll end off by saying that I am watching the evolving design for this particular router as it is running parallel with mine in the size but not the design, and I am weighing up the design concept in case I am on the wrong track in any aspect.

Mine is going to be made from cut plate material as opposed to extrusions, but both are with a moving table.
Ian.

[G59]

handlewanker, my apologies. I had you confused with someone else.