[johnnyb]

Jason, you do not get any whipping. The lead screw does not turn, the nut turns. This was why I went with the spinning nut.

John

[johnnyb]

mrgadget, I used 1-3/4" aluminium bar stock that I had. Cut about 4" long turned down about 3" of the bar to 7/8" to fit the 2 bearings (not thurst bearings) I had. I think the bearings OD was 1-5/8", I knurled it the width of the timming pulley and bored a 7/8" hole through it. Got the timming pulley from McMaster Carr they are plastic with an aluminium insert 1/4" ID I pressed out the aluminium insert and bored the pulley to 7/8" (this was the tough part because there is not much meat left, and the reason I went with a larger OD pulley). I then epoxied and pressed the pulley on the shaft. Drilled and tapped and attached the HDPE with machine screws. Turned down the HDPE to the same diameter and tapped with a home made piece of 1/2-10 acme rod. I used MDF to hold everthing, used a forester bit to drill a 1/4" in each side of the MDF for the bearings. I made a collar to hold it all together. I was happy with it except the MDF part, my new design is all metal and uses a piece of pipe with a bracket welded on it and bored with the bearings pressed in. I was using the design for my X axis and Y axis. Most of the work was done on a 9" lathe.

[handlewanker]

Hi all, seeing as how rotating shafts will vibrate and whip, and the alternative of rotating nuts also have their problems no matter how you look at it. Has anyone given a thought to rack and pinion? I mean twin rack and pinion, one either side of the X axis rails, to keep the table square to the frame, and each driven by two synchronised steppers, positioned midway to give a equal travel, fore and aft.
Alternatively a cross shaft driving two racks attached to the table and driven by one stepper direct coupled with gearbox.
The rack and pinion is as per dial calipers and should give smooth travel if depthed correctly and alligned. This will give all the budding design guys a chance to see what they are made of.
The stepper motor drive would have a reduction gearbox integral to give the resolution and torque to achieve a reasonable high speed traverse.
The rack would probably have a 4mm pitch and a drive gear meshed with it of 20 teeth.
This would give 80mm travel for one rev of the gear. The gearbox would need to be in reduction to allow the stepper to operate at full speed and give the necessary torque and resolution.
The rack does not necessarily have to be a straight sided conventional rack as an Acme thread will accept a drive gear as long as it is mounted against a suitable backing plate for support.
Using the Acme thread as a rack is not a new idea, and would be a very economical off the shelf rack source. It could be mounted by machining a flat on the back side or just seated into half round pillow blocks with screws from the back. The gear just needs to be firmly mounted so as to give continuous engagement with the rack.
One picture is worth a thousand words here, but I haven't worked out how to attach images in this forum. Perhaps someone can give me a pointer.
Ian.

[Madclicker]

Do you have the source for acme nuts to use as a pinion for acme rod?

[handlewanker]

Hi Carel, been looking at all the answers to the drive problems of the long leadscrew. Just one thing comes to the fore, If you are going to entertain the idea of using a rotating nut, then it would have to be in conjunction with a ball leadscrew.
I've seen mention of an acme screw but if you consider the wear and tear and power needed to run this up and down, and the backlash problems, then it is ludicrous to even consider this method.
So we are left with the ball leadscrew. Now surely this is a bought in item and if the project is a DIY design concept, where do you actually start to make the parts as a design concept
I would imagine that the stepping motor in conjunction with the rotating nut direct coupled in-line would be the best solution, even adding the extra weight, and this has already been designed and marketed, although rather pricy.
Redesigning to use an acme screw, and adding a drive belt? I ask you is this logical? It may be in the capabilities of the average machine builder, but how would you maintain accuracy?
Backlash destroys any semblance of accuracy when going back and forth. You can't add anti backlash nuts to the screw. They only take up a bit of the play but you must have a running clearance.
So now we come to the great conundrum, how much accuracy do we want? Has anyone with a large flat bed router ever had the co-ordinates calibrated? By this I mean, for example if you were to plot four points at the extremeties of the machine's drive path in an X and Y path how accurate would they turn out. How square would they be? Would the dimensions measured over the points be as plotted? And you want to consider an acme nut drive?
Ian.

[handlewanker]

Hi Jason, I see that you are using the spinning nut arrangement. Would it be possible to have a small airpump attached to the X axis carriage and arranged to only come on when the nut motor is activated and so blow the dirt off of the screw?
If the screw is coated with lubricant, and also dirt then this probably wouldn't work, so a rotating brush would be needed.
Another method comes to mind that I saw somewhere else, a canvas strip about 4 " wide and coiled up in a spring wound drum and attached to the carriage gets pulled out as the carriage moves forward and is pulled back as the carriage moves back. One for each side needed.
Ian.

[project5k]

i was chasing this same dust on the screw issue, and it was suggested to me to get an old slinky stretch a stocking over it and attache it at each end...sounds like a plan to me, if you use the plastic slinkey that is

[fkaCarel]

Hi Handlewanker. First, I have'nt got a single stake in the rotating nut industry. If people want to make routers with CNC controlled jet propulsion, fine by me, but rather not in my street. So lets walk the pro's & con's of a rotating nut:

If the nut is well made, meaning 2 bearings and well made as in concentricity, well assembled as in line with the leadscrew, I see an advantage for the rotating nut, because the leadscrew is not any more constantly seeking for guidance, because of it's inbred eccentricity. It's not push/pull anymore, but pull/pull. I like Constant Conditions.

As for making: there are people who have money, there are people who have time and there are people who have both. So it is possible there are people with time and no money making very large routers. If they can save some money with our help or advice, we help them. I can even understand there are people who want a rotating nut, just because they want a rotating nut.

Backlash and more to that anti-backlash is a loaded subject. If I remember clearly you are a spring-loaded antibacklasher. I keep my meaning to myself. There is also a thing as backlash-compensation, which is also used in conjunction with ballscrews. I worked on a very expensive ballscrewed lathe, with 0.07mm backlash on X and Z. Was not a problem. From my point of view the real backlash problems arise from computer generated paths. They don't follow necessarily the logic, applied when you have a lump and make it following your experience.

The great conundrum: I am a metalworker and so are you. We are just sick. The everyday working in 0.01mm or below, disqualifies me for woodworking, or the other side of the sprectrum: building. Where a builder is proud, a metalworker gets dizzy of all the deviations. Some like to measure, some like to fiddle.

I made 20 years ago a 1*1mtr CNC router with a friend. Pre-internet:1986. Trapezium rods, no special nuts. I visited him this afternoon and we had a look at it. Nothing mechanical is renewed since it was made, and it still functions well, and he made a fair amount of money with it.

[project5k]

well i like the thought of a spinning nut cause i believe that with the thin screw that i have, i can actually get more speed out of it and avoid the whipping issue... plus it just sounds like a fun challenge... i'm in the got time and no money category, i have 2 lathes, no mill, lots of hand tools and a pretty good imagination.. so im gonna give it a shot and see what happens, as with all things new im sure that i'll mess up a time or 2, but look at the fun of tinkering, and things that i could learn while doing it.. besides, i just love being out in my new shop, 2400 ftsq to play with no wife, no dogs, no neighbors, just me my tools and my imagination... oh yea, and about 1000 watts of sterio with all my favorites loaded in a 301 disk cd changer......

[Geof]

.....you are a spring-loaded antibacklasher....

Totally off-topic so anyone is welcome to abuse me .... but I think the phrase above taken out of context, all on its own, sounds like a great insult.

[fkaCarel]

First of all, I would propose to ban the Dutch from this forum, because their lack of ability to write proper English can always be interpreted as an insult. Other country's to follow. As antibacklash now is lifted to a religious level, as I intended to, every member has confess his belief. As: I am a split nutter, a double nutter, a compressed nutter, a spring loaded nutter, a ballnutter, a double ballnutter, oversize ball ballnutter or just nuts.
Hi: I am Carel and I believe what suits me.

[fkaCarel]

Forgot rotating nutter. Excuse me.

[project5k]

i think your all nuts, but thats why i like it here, i finally found somewhere i fit in

[fkaCarel]

Well, welcome to the lunatic asylum. Be gentle to the nurses and psychiatrists, they are there to help you and don't forget the medication. Don't chew the chips.

[project5k]

so lets get back to the spinning nuts... im just wondering if the life of a delrin or whatever kinda plastic they are, will increase or decrease by spinning the nut rather than the screw, i would think it wouldnt change..same forces, same spin rate, well ok maby faster, but what do i know.. the one benifit to having a fixed nut would be to drill a small hole in it and have some kind of drip lubrication on it at all times... but as for spinning the nut... i was thinking that i would have to come up with some kind of carrier, and then the thrust bearings, and axial bearings.. hmmm this could get real complicated real quick without a mill...

[fkaCarel]

Well I will give you some ideas. Think of the bearing system you have now. Increase the bearing size. Think metal as you now get a nut axle. Think round (lack of mill), because you need only a hole where the belt comes out. That is in essence 3 parts.
If you have a lathe, you have with a little imagination also a mill. The lathe is the mother of all machines.

[Pxsi]

If you go with the method mentioned earlier and attach a timing pulley to the outside, I don’t see why you would need a mill. Start with a tube that you can turn the nut to fit inside of, and then bore out your pulley to a press fit like mentioned earlier, and then press angled roller bearings in to the ends.

Other than drilling and tapping some set screws all operations could easily be done on a lathe.

This is starting to sound like a fun project; maybe I will have to give it a try.

I don’t see how this project could be all that much more complicated than turning and mounting bearings on the ends of a timing belt driven lead screw. I suppose it depends on the person and the tools they have.


Pxsi

[project5k]

hmmm tapered temkins? hmmm wheel bearings... hmm cheap, easy to get, replaceable races... about the right size....definately carry the load.....

got lathe will make swarf!!! you know tho, you say that the lathe is the mother of all machines, and i have 2, a baby and a monster, and i'd trade one of them for a decent mill on any given day... to me the mill is the biggest baddest mamma of them all, oh what i wouldnt give for something like a bridgport, heck, i got a deal for ya, i have a 1985 goldwing i'll trade for a good condition knee mill, or, hmmm ive also got a 97 honda civic, new upper end 5spd manual, gets something like 32mpg.... mostly highway miles from seguin to austin..... but you cant have my truck or my scion...... any thoughts?

[project5k]

ok, so after i drew this i thought about the forces that the belt are going to put on the bearings and im thinking that a redesign is in order so that the pullie is between the bearings... but anyway, this is the basic idea... whaddya think?

[Pxsi]

I like your design. I would defiantly moving the bearings to the extreme ends, that way you can sandwich it between 2 blocks.

You will properly need to add something to bolt the pulley to so it doesn’t freewheel on the tubing. Would could; bolt, solder or weld a disk to the outside of your tubing to bolt your pulley to. Just make sure you turn the edge square so your pulley does not wobble.
We all hate wobbly pulleys. :stickpoke

Pxsi