I have an assortment of questions regarding fixed lead screw and rotating lead nut configurations.

Everyone seems to use timing belts on lead screws. My local Harbor Freight type store (Princess Auto here in Canada) has an excellent selection of small sprockets and chain. Is there an advantage to timing belts and cogged pulleys? I think I could adjust the backlash out of a chain system.

How much side load can I put on a stepper output shaft? I'd guess most steppers use bushings so they may not stand up well to significant side loading. Do I need to plan for a side load support on the motor side, in the event I go with a rotating nut system?

Does anyone have pictures of a DIY implementation of a rotating nut system?

I really like the idea of direct drive lead screws. I'm just kicking this around. It would really be a sweet idea if someone made a hollow shaft stepper that could act as both stepper and nut both.

Just did a simple sketch as a worst case scenario. Imagine a 4-tooth chain sprocket, not realistic, but is calculates easier. The line of the chain is horizontal. The sprocket is in the "X" position. The chain is now lifted during 45 degrees, if you move the chain. This means that true anti-backlash is not possible with a chain. A timing belt has chords, outside the pulley, that are driving. The tooth are actually just anti slip. So a timing belt gives true rotation transfer, a chain not.

A stepper is a motor, it should be designed to transfer at least it's output.

Just did a simple sketch as a worst case scenario. Imagine a 4-tooth chain sprocket, not realistic, but is calculates easier. The line of the chain is horizontal. The sprocket is in the "X" position. The chain is now lifted during 45 degrees, if you move the chain. This means that true anti-backlash is not possible with a chain......

This effect is somewhat analgous to the non-constant transmission of rotary motion through a Hooke coupling universal joint running at an angle. The effect can be countered by putting two universal joints out of phase an what I think is called a Birfield coupling. Would it be possible to use two successive chain drives out of phase to compensate for the non-constant chain transmission?

I saw this pic in one of the forums but cannot remember where, maybe ger21 can help.

Jason

It's the same as the rear drive axle from gearbox to differential (Hooke = Cardan?), double the system and offset the sets halftooth. Invent wearfree chain and put new batteries in your calculator, where you could have used a timing belt in the first place. This is just one the uses of geometry, where you see error introduction. In practice, you may never see it, or on the other side, you may never find it, if it bites you.

What about something like this, i guess it wouldn be that hard to fabricate. 2 bearings 30mm inner diameter, a deldrin or aluminium rod, bored and taped to fit the leadscrew, and a standard pully turned to fit the rod

I agree on the double bearing, the picture in post #4 leans on the shaft. I disagree on delrin for a bearing fit or aluminium for a nut. Bronze would be a better suited material. And the design should be expandable for anti-backlash. The difficult part in designing rotating nuts is, that there is almost the need to design space for spare belts, to avoid large scale disassembly.

Bronze then, as long as its soft enough to tap:-) My guess is that with a normal router for hobby usage the belt will last "forever", anyway you have to remove it from the rod to change belt so a few screws should'nt make a different. Maybe this inclosure would work

....(Hooke = Cardan?)......

Courtesy of Google:
simple universal joint, known in English-speaking countries as Hooke's joint and in continental Europe as a Cardan joint,

So when you communicate in English you have to use Hooke but any other language you can use Cardan.

On a bicycle you have to remove the wheel to change the tyre. Replacing a belt on a rotating nut is the same, with all the accompanying alignment problems.

So when you communicate in English you have to use Hooke but any other language you can use Cardan.

This forum keeps on improving my technical English. I have to thank everyone, and especially you, Geof, for this. Sometimes when reading this forum and at the same time being confronted with people from the American continent asking for directions in the only language they speak and expecting us to speak it too, I tend to misdirect them. I promise you all will get correct guidance from me. Code: "Do you speak Ballscrew?"

Maybe this could do as an AB solution, just add a spring in between the 2 parts and tighten. No idea if it would work, but it looks like some of the other solutions i have seen around here

i too have been considering using the spinning nut approach, my plan was to build something very much like whats in post #8, but with the double bearings like post #6... my question is this, when you spin the screw, there is a chance of the screw whipping if you spin it too fast... is there any chance of this type vibration by spinning the nut, or are you only limited in speed by your bearings, motor and gearing?

With the rotating nut the mass is a constant, no matter the length. So at a certain moment, to be left at the imagination, it is a better solution, traded for complexity.

You mean a hollow shaft stepper something like this?
http://www.eadmotors.com/default.asp?sel=Linear_Actuators_Desc.static&secid=5&ftype=products
Or this:
http://www.portescap.com/6.cfm
Or this:
http://www.hsi-inc.com/

Neatman

Hi Guys

Just in case anyone is interested you can get CAD models of the profiles for the pulleys from Gates for GT2 and HTD

http://www.gates.com/designview/index.cfm?location_id=866&go=PT2CAD

You just have to register etc etc.

I have toyed with the idea of rotating nut designs and I realised that for a 15mm belt width you could split the pulley into 2 halves leaving a gap in the middle for adjustment of backlash. The great thing about splitting the pulley into two halves (as opposed to 3, 4 or 5 halves lol) allows you to machine the profile directly into the two parts of your adjustable backlash unit. From memory to finish the profile all you need is a 2.5mm diameter cutter with around 8mm of exposed shank. It wont matter that the flute length is less since you would make it from acetal (not Delrin guys, Delrin is a trade name of Dupont for acetal) and a bit of rubbing on shank isn't going to hurt. I'll post a picture tonight when I get home of my preliminary design.

Anyhow the point of this post is that you can machine your own GT2/HTD profiles to integrate the 'pulley' into your rotating nut design.

Cheers

thoes are some really cool motors, i really like the pass through design, but i would worrie about maintainance of the nut and so forth...

Hi Guys

Picture of concept rotating nut design as promised. The design is generic enough to be adaptable to whatever nut/screw combination you want. It is half finished but with a little imagination you can see what I am trying to achieve. The parts I haven't added yet are the two deep groove bearings at each end, the separation springs, the nyloc nuts and bolts to hold it all together and the drive nuts. The basic idea is the separation springs push the nuts against each extreme of the thread and the bolt and nyloc nuts allow you to tune that separation so that it just gives a teensie weensie bit of clearance which would be taken up by grease. I was planning to machine it from acetal and press fit brass nuts (probably trapezoidal thread) into the nut housings which are also the pulley halves. The sleeves are to keep the two 'halves' aligned. Being machined from acetal would make the unit very light to rotate. The nut housing/pulley and the bearing adaptor is used twice in the assembly. There are 36 teeth on the pulley.

Cheers

Hi, just a quick observation, if you spin the nut and lock the shaft then you have to add the weight of the drive motor and trailing wires to the moving carriage. The inertia loads will cause problems as the weight increases.
One important rule: if you're going to change things then you'd better have a very good reason, for to change things for no reason at all is amateur.
Ian.

"change things for no reason at all is amateur", strongly depends on what your goal is, for most people here i guess its to explore things and trying different solutions, so i wouldnt agree on that statement

Guldberg: I agree with you. You make no point by bringing in the word "amateur" with the implication that you are an professional. I know enough to know that I am an complete incompetent amateuristic amateur!;)

Hi Guldberg, didn't mean to ruffle anyone's feathers, by all means think outside the square, use lateral thinking, that is if the resources are plentifull and the object is to do a bit of exploring and experimentation.
It takes a fair amount of time and effort to try something radical or different. I always hated getting halfway through a project and then seeing an alternative method that just might be a better approach. That is why some jobs don't progress beyond the drawing board because there is always a better way to do it, commonly called development.
To sum up, use your common sense and rely on your intuition. That's what experiance teaches you.
Ian.

From SKF news: Long Lead Ball Screws feature rotating nut design.

March 3, 2006 - Ranging from 25-50 mm dia with leads from 20-50 mm, Series SLT features rotating nut with axial play, while Series BLT includes backlash elimination. Design allows drive motor to move with nut to minimize inertia and achieve linear speeds to 110 m/min. Rotating nuts realize max transmissible torque up to 803 Nm and max transmissible axial load up to 162 kN, depending on type. Applications include packaging and automation systems, laser cutting, and production machinery.

Handlewanker: The inertia loads will cause problems as the weight increases
There are many roads to Rome.

Hi, you want to take a mortgage out on an SKF nutdrive? I can think of better ways to cost a job. Fascinating though it appears, alternative thinking has to have that bit of forward thinking that determines rationality, and not to be carried away with flights of fancy. Agreed there are many roads to Rome, but I'd rather fly. Remember Ockam's razor, "when all things being equal the simplest is always the best".
Taken to it's broadest interpretation in this instance, I would rather consider a direct drive of stepping motor and ball leadscrew with an inherent lack of backlash and all the drive components static mounted, than putting all the drive components onto the carriage to be moved.
One problem with driving the nut is, if it is driven by a toothed belt, how do you change the belt when it breaks or wears out? That is assuming that the nut is between the bearings and not cantilevered to the side.
The other other consideration is how do you couple a drive motor to the nut? Toothed belt is one way. Direct drive is another where the nut becomes a part of the drive motor armature, or if the nut is driven by a gear train then a complex anti backlash mechanism is required.
There is no simple answer to this last solution as you have to remain in synch both forward and back.
I had thought of what if the rotating nut were to be mounted to the middle of frame and the leadscrew attached to the carriage ends and was the only component moving back and forth. Good luck if you think this is the best way. Another way, yes, an alternative way, yes, but a better way, I wonder?
I like new inspirational innovative ideas and will always seek out new ways to solve a problem, but at the end of the day you have to evaluate the merits of any solution be it on financial, availability or just because it is new and not been tried before and seemed like a good idea at the time.
Ian.

No matter the price, earlier in this thread I wrote that a rotating nut comes into play when you get for example length/rpm problems. I also mentioned the replacement problems. You just need some more words to repeat it. I just want to ask you to be friendly and not to instantly chop things down. A rotating nut is not a inspirational innovate idea, it's an engineering solution.

im considering the rotating nut because i believe that i can build it with the materials and skills that i have cheaper than going out and buying another 72inch screw of a larger diameter... i believe that i am going to have speed issues, due to rpm limitations on my screw... its a plausable solution that i'm going to chase. as far as belt replacement, i just dont think its going to be that big of a deal with the way im going to set mine up, first of all i intend to have a spare belt cubby built into the mech, so that if the first belt were to fail, all i would have to do is crawl under the machine with a couple allen wrenches and a pocket knife or a set of dikes, cut off the old one, and slip in the new one(that would be around the screw all the time but not in contact) and besides, whats the lifespan on one of these belts, i just cant see it failing that often, but that might be my lack of experience showing

The rotating nut approach is the Holy Grail of leadscrew design. The one single problem that haunts the spinning lead screw is the limitation on speeds imposed by the length and diameter of the lead screw. By spinning the nuts you can get amazing feedrates. The REALLY fast commercial machines that need both accuracy, min backlash and high speeds use the spinning nut approach. I really do like your approach for the antibacklash. I have sketched up several ideas for using a conventional ballnut-screw combo or one of the anti backlash nylon types. I also like your idea of spare belts on the shaft. Good Belts don't wear out that fast but in the even of a jam and with larger servos I have seen the teeth on belts get ground off (Cheapest thing to break in the drive chain).

Keep up the work.

well, while i would agree with handlewanker that adding the motor to the moving assembly will add some weight, i would have to think that at least in my case adding a 3lb motor to the gantry would be far less inertial load on the motor itself than would be the spinning screw... by the time you figure friction alone, spinning the nut seems more efficient, thus requiring less motor to go the same speed... while i will be the first to agree that the spinning nut design is by far more complex, i think if done properly, would actually be cheaper in actuall $$$, less motor, less driver board, fewer bearings, (figuring a double bearing on each end of the screw) SMALLER SCREW!!! and i capitalize this because according to everything that i can find, you will have rotational whip for a certain size screw long before you get close to its coloum strength, so thats not an issue... and pluss, the way i look at it from a structural standpoint, by hard mounting the screw you could pre tension the screw just a little and cause it to be even more rigidly held in place... just a thought anyway

The main advantage is that both directions are pulled, if you design it that way, by boxing the spindle in. And belts don't wear that fast, just do a little overdimensioning. If you would insist on having a spare belt ready, you may compromise the design to much. Good luck.

i dont follow boxing the spindle in.....

Hi Carel, It looks like the only reason a long (20mm X 2M) leadscrew is giving trouble is the vibration caused by whip. Wouldn't it be better to design the whip out than go to a more complicated method? I know rotating nuts are used for certain purposes, that's why they sell them.
Ian.

English and technics will always be a challenge for me. If you preload the spindle, you pull on the spindle. The reaction on this is a push on the support.
If its not rigid or structural enough it will bend outward or inward. So this must be beefy and symmetrical.
>--pushsupport--<
<---pullspindle--->
>--pushsupport--<

Handlewanker: The problem is that long spindles always will vibrate. They are not straight, so they amplify their runout. He's talking about 72 inch. That's almost 2 metres. If you hold such a length in your hand, it's like a fishing rod, you will see it bending. So if you have the power for rev's , the rotating nut is worth considering. If he wants to use trapezium or Acme thread, I would start with buying 2 nuts, and design from there. From my point of view, it's not that difficult. It's only tedious drawing, turning, milling, tapping and assembly as usual.

..... It's only tedious drawing, turning, milling, tapping and assembly as usual.

But if you are doing this kind of thing as an amateur or a hobbiest isn't this the fun part?

It is only tedious to us poor souls who have to do this day in day out to make a living and put bread on the table:violin:

I meant the lengthy meaning, not the boring meaning of tedious.

And never forget the pride, whether you earn your bread with it or if it costs you your bread, of a selfmade, selfdesigned, flawless working assembly!

Hi all, the photo in post #4 is mine. I was using it on a MDF machine with a 6' X axis the feed screw was 1/2-10 acme and the gearing is 1:1. I am currently rebuilding my mdf machine. The new machine is all angle and 1-1/2 square tube. I am still going to use the spinning nut on my X axis but the bearings are now pressed into a piece of pipe that's been bored out. The spinning nut worked well the one thing I did discover (solved in new machine - I hope) is that the feed screw doesn't spin so dust from cutting just sits on it and builds up, could make a wiper or place the feed screw under the table out of the dust. I didn't notice any backlash the nut was HDPE I think and wears well.

John

well the end product, a working machine, is my ultimate goal, getting from here to there is just as good for me....so i say ON WITH THE TEDIUM!
besides, just think about how much you learned in the process...

I think your design is vary smart. I have seen kits that do what you’re talking about for X2 mills. The problem with them is that you do not have enough room under the table to put a decent nut so they put it on the end of the table and firmly attach the screw.

You may be able to side step your added weight problem by doing something unconventional. You could attach one end of the screw to the gantry and put the nut in the end of the axis. This would make the screw come out the end when it moves to the one end. Depending on your shop setup this may or may not be a big problem. You would want to attach some pipe to the base for your screw to telescope into. This design would be great for a vertical setup, as long as your ceiling is high enough. The other advantage of a vertical setup is that the mass of the gantry becomes an anti-backlash mechanism.

Take this advise with a grain of salt, as I am a mill man not a rougher man so I have not even achieved amateur status. :stickpoke

Pxsi

Hi all, the photo in post #4 is mine. I was using it on a MDF machine with a 6' X axis the feed screw was 1/2-10 acme and the gearing is 1:1. I am currently rebuilding my mdf machine. The new machine is all angle and 1-1/2 square tube. I am still going to use the spinning nut on my X axis but the bearings are now pressed into a piece of pipe that's been bored out. The spinning nut worked well the one thing I did discover (solved in new machine - I hope) is that the feed screw doesn't spin so dust from cutting just sits on it and builds up, could make a wiper or place the feed screw under the table out of the dust. I didn't notice any backlash the nut was HDPE I think and wears well.

John

What speed were you able to achieve without whipping?

Jason

johnnyb, would you mind sharing some info with us on your spinning nut design you used on your machine? Great design BTW. I'm looking to implement a spinning nut on the machine I'm designing on the x-axis since it's around 5 feet in length.

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

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.

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.

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

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.

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.

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

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.

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......

.....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.

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.:D

Forgot rotating nutter. Excuse me.

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

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.

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...

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.

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

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?

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?

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

The first coming,i know little about cnc machine,I think the forum will be helpful to myself.I am very pleased to be here.^-^

well actually in that drawing, the bolts that go through the delrin nut also go through the pullie, and then are threaded into the aluminum that the bearings are on... so that would stop the wobblie pullie and keep if from freewheeling..... maby tonight i can redraw it with the bearings sepperated......

Hi Guys

Picture of concept rotating nut design as promised. The design is generic enough to be adaptable to whatever nut/screw combination you want. It is half finished but with a little imagination you can see what I am trying to achieve. The parts I haven't added yet are the two deep groove bearings at each end, the separation springs, the nyloc nuts and bolts to hold it all together and the drive nuts. The basic idea is the separation springs push the nuts against each extreme of the thread and the bolt and nyloc nuts allow you to tune that separation so that it just gives a teensie weensie bit of clearance which would be taken up by grease. I was planning to machine it from acetal and press fit brass nuts (probably trapezoidal thread) into the nut housings which are also the pulley halves. The sleeves are to keep the two 'halves' aligned. Being machined from acetal would make the unit very light to rotate. The nut housing/pulley and the bearing adaptor is used twice in the assembly. There are 36 teeth on the pulley.

Cheers Now that looks like a solution for my "Z" axis! Thanks for posting the image :cheers:

Hi Carel, we love the Dutch.Wouldn't dream of banning anybody. If you've got a point of view, let's hear it. An idea no matter how ridiculous may trigger off another idea and solve somone's problem, and we don't mind if you put a bit of Dutch magic in as we like a laugh too.
I reckon if everyone contributes their experiance and thoughts we'll all get along. Moral:- think twice cut once.
Common problem is how to make your nuts spin and not get backlash. If backlash can be compensated for to be almost neglible then we'd like to hear how it is catered for in the X Y profiling where the table is required to go back and forward, and not cause a problem. How much backlash are we experiancing?
I know that I get .5mm on my Bridgeport, but that is normal milling not CNC, and as there are compensating nuts on the X and Y axis leadscrews, then it's easy to adjust. My lathe is not so lucky, a 1/4 turn of the crossfeed screw is about normal (no compensating nut), and this is about .025". One day I'll make a new nut with a back up nut.
Ian.

Hi Project 5, re post #58, that goldwing must be worth a bob or two. I saw a whole lot of Bridgeports being auctioned on the USA Ebay site for around US$3k -US$4k. Have you tried any of these? Even if they're a "bit used" they're still good.
I bought my 'port from the firm I worked for when they downsized the toolroom in '97, and that was 20 years old then. After I bought it, all the guys in the toolroom said what a fool I was as they only got rid of the ones that were worn out.
Well I paid A$3K for it, and 4 weeks later when all the stuff was gone I started to get offers from the other guys, above the price I'd paid, for the "worn out" junk I'd bought. We were all into backyard sub-contract work, and I guess the others just missed the boat.
That was '97, and I still have the mill, and all it took was a clean up and adjustment of the gibs and nuts. At the time in our toolroom, if a mill didn't have a DRO or auto feed, then nobody used it.
Ian. (have mill use to travel.)

Here you see my corcern on this forum, and probably the internet in general:
http://www.cnczone.com/forums/showthread.php?t=24669&page=3
If I help with a maybe sound design, it will be burned down, just for the sake of burning down. No motivation, just SWAG in reverse.

My satisfaction was today's newspaper, mentioning the university of Amsterdam had let a cartoon drawn by one of our famous cartoonists. It was heavily protested by a Canadian guest teacher. She lost. Comment of the cartoonist agent: "Canadians don't have a sense of humor".

Nevertheless, I've had it.

um... ok you lost me dood, if you have a suggestion on how to make the rotating lead nuts work, then i'm interested in hearing it, and if it seems sound, and is within my abilities, i just might try it... but i have no idea what stalling in a toolpath and something about a cartoon had to do with anything....

Was I in an alternate universe for a second there?

I would like to see your new improved nut design. I would also like to hear how it goes when you get around to making it, I have an upcoming project that will most likely require a spinning nut. Any input of what does and doesn’t work in the real world could save me a lot of time.

Pxsi

Hi Kipper

I hope you do build your Z-axis based on my design. I would love to see it in action. I'm too busy at work and too busy raising 3 monkeys and then combined with too lazy I'll probably never build it lol. I may even finish off the design and repost now that I know someone is interested.

Cheers and go the swannies!!! (its AFL grand final weekend here in Oz)

i will definately post my findings if and when i build a spinning nut system...