For The Z or any other axis you cannot rely on a ballscrew to take any lateral load (at all) only a pure as possible long axis load is permissible.
You will need a pair of rails to carry the load. One ballscrew is fine sized according to the long axis load carrying capacity you will find on the manufacturers specification. Bear in mind the impact hammer will apply a large dynamic load to the ballscrew, You may need to use a higher rated screw to cope with this. I would contact the screw manufacturer and ask for advice.
When setting the rails and ballscrew up they must be perfectly collinear or you will be applying a forbidden lateral load as the paths interfere with each other.
How does 2 screws same length give extra travel.? Edit: Ok re -read under stand now 2 ballnuts in parallel is less length than 2 nuts in series.! But still bad idea as it will be quite hard to ensure preload is correct to give zero backlash.
Unless your spinning the ballscrew at very very high speed then at this length vibration shouldn't be problem if supported at both end. If your really bothered then use fixed bearings at both ends and tension the screw.
Personally I would just use fixed at both ends with tension and double ballnuts, this will be more than enough.
John I don't think Boyan is trying to use ballnuts to increase strength just lessen backlash and vibration/whip on screws.!
Last edited by JAZZCNC; 14-08-2014 at 07:54 AM.
Reflecting on the dynamic load applied to the ballscrew by the Impact tool.
For many reasons I would prefer to use timing belts instead of ball screws. They do not suffer brinell pitting damage
This search came up with some useful links.
I built this router with timing belts (The Z axis only in this machine is a ball screw but that could be changed)
I know the budget is finite but would it be possible to make a belt driven machine Or two machines One for impact work and one for Routing? Maybe sharing the electronics?
This Is the Router I built with a mate using timing belts for a non profit Men's Shed. http://www.machsupport.com/forum/ind...?topic=23730.0 There is a small video. It works really well and is used by the group so much there is a waiting list.
Originally Posted by John McNamara
-Yes, we are talking all the time of long axis load. There will be no side forces or if there will be, they will be smaller than say cutting aluminum.
- the dynamic load of the hammer is not big at all, as the head of the hammer will be small, anyway, the hammer can not produce such a force as one can suppose.
-The collinearity will be way under specifications of ball screw or rails manufactures. I can easily make them collinear to something like 0.00mm
Ok, thanks for the input.
Originally Posted by JAZZCNC
The design as its now and i have the elements already at home, implements that the both screws have fixed bearing supports at both end.
So you say there will be no sense to make the design as you suggest with one ball screw, 2 nuts and 2 and 2 fixed bearing supports at both ends? I mean only one fixed end will be enough? The bearings doesn't seem very big to me.
Originally Posted by John McNamara
I know about the ball deformation. It doesn't bother me though. The hammer head will be half 10mm diameter circle . The air in the hammer dampens the hit, the material is very stretchy too/1-1.2 mm normalized sheet/ , the whole sheet stretches also, not only at the point of hit. More or less the hit will equal to 1 bearing ball hitting the material. This would be spread to all the bearing balls in 2 ball screw nuts. I am not sure how many are they. means that its not like a hit on hard rigid surface
I was contemplating this belt driven. What i want right now is the following. To finish the machine as faster as possible. To try the hammer thing at least once. to draw conclusions and not break the precision of the machine in that process. To use the machine right away to make a new one, simpler, with homemade ridgid elements, belt driven as you say and most importantly 5-6 axis. I almost have all elements for a new machine, apart of this one.
You miss under stand me I think.? . . . . . I would use 1 x screw with 2 fixed ends and tension the screw and if backlash was important then I'd use 2 ballnuts.
Originally Posted by silyavski
Correctly sized screw will have no issues with this setup if the forces are small like you predict.
Dean thanks for your time!
Originally Posted by JAZZCNC
I started already redesigning it to go with one screw and 1 or 2 nuts as you suggested. That will save me for a beer or two. I understood you correctly, but messed with my English.
What i meant is if there would be additional benefit if i fix that screw both ends with double fixed end supports, meaning 2 supports each side chained together and then tightened by the nut at the end.
I have seen Pre tensioned ball screws in large CNC machines, Also many where one end is fixed in preloaded angular contact bearings While the other is allowed to float in to allow for changes in temperature. The floating setup may be a less difficult setup to use, particularly if the frame is lightweight. If you pre tension you are imposing a substantial load on the frame, It would have to be stiff or it may be deflected out of alignment by the preloading stress, and the deflection would be likely to vary with temperature.
Silyafski, I really don't know the first thing about making those drum surfaces but the other day I saw this video and thought if this kind of forming process might not work for you as an alternative to hammer forming the sheet metal.
Exactly. Thats one of the reasons i made such strong Z and the cheese holes on the Z. I will not push the spindle bearings, instead will fit it somehow directly to the boxed Z.;
Originally Posted by mitchejc
Some updates. 2 very hot weeks, especially if you are working alone in 70% humidity, 40C temperature and soldering all day long +weekends and moving heavy stuff.
Had to clean all stuff from the garage. Draw white lines for the footprint. This machine will take a lot of space. Of course it rained right after i took everything out, did i tell you it hadn't rained like 11 months.
Started with the gantry. decided to keep sides square, so later could flip and support easier the gantry. Do you see the blotch further on the floor. Guess what, just before starting all my boxes with paint fell on the floor and some spilled. A little diversion :-)
I have mixed feelings about the Evolution saw. While the motor and blade is great/made in japan/ the saw is very very flimsy. Next project will be to throw away the base and do a new one. I wish i have bought the Makita. It was 100eur more expensive and don't come with blade- another 100, so thats why. Anyway, an essential machine for the project.
Ventilator to cool myself and change of plans. The 60x60 profiles cut to size that were meant to support the rails were discarded. There was no way i can solder them from all sides. Instead i cut all of the 60x10 plate/6m in total/ and decided to separate them by the 60mm using at least the profiles i have already cut. Some carefull soldering from here and there. Very rigid result.
As you see from the pictures above everything is soldered till the end. Now there was another momentary decision. No legs for now untill i decide something clever and the steel from the legs went just inside the sides of the machine. So stair like sides with no holes, there lie the rests of the profiles meant for legs.
I cant explain how strong that machine frame feels. Including that bestial gantry. Vertical bend or twist- i did not even bother to measure it with the indicator. Its solid as a rock. starts to look like a Frankenstein thing from movie.
So today i finished working at 20.30 and couldn't help but move all elements with last available effort, as i wanted to see how it would look. I am a strong man, no lift or whatever help, so i am becoming stronger moving all day these pieces around while soldering. Did i tell you that all the soldered pieces weight around 500kg .
So here is my baby. Its huge. I am a bit surprised how big that is. Still has no name but i think it would be something military:
So after ~15kg of wire, 2 CO2 bottles and some crazy days i start to see how will look. Still have no color in mind.
Last edited by Boyan Silyavski; 06-09-2014 at 10:17 PM.