Quite an Unusual one

[John McNamara]

Hi Silyavaski

You have been busy with CAD, nice drawings, what cad package are you using?.
And great to see you have assembled the parts and drives....
How do you intend to join all the steel sections and the vertical bracing? By welding?
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From memory you are going to use this machine with an impact hammer to make musical instruments.
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Will it be an air operated hammer similar to one of these? https://www.google.com.au/search?q=a...w=1215&bih=817
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I was using a small one hand one last week to break up some concrete. they cam deliver quite a blow, You can turn them down by using both a pressure and flow regulator. the settings will depend on what sort of material you are acting upon. even at a low setting the energy released is significant.
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Tubular steel is very strong no doubt, however it can vibrate, particularly if the hammer is set to oscillate near the resonant frequency of the frame. Without very sophisticated FEA software it is hard to conceptualise just how a structure will behave. however you may find it advantages to consider the issues involved in advance and if vibration turns out to be a problem have a means of increasing the mass of the structure and what sort of damping measures you take to reduce the amplitude to an acceptable level.
.
Here is a link to an excellent paper on concrete filled steel structures used in machine design. http://www.mech.utah.edu/~bamberg/re...e%20Design.pdf
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Regards
John

[Boyan Silyavski]

Hi,
Now the question of the day is having in mind all the servos are 400w, do I drive all 1:1 or 2:1 ??? The x y encoders are 2048 and the z is 2500 ppr ,all the screws are xx10 and 1605 for the z
The servos will accept 100000 pps at step mode

[Boyan Silyavski]

Last revision. Can not find a weak spot that is not bombproof. Starts to look more and more like a mill .

1. Decided to drivel all 20:30t, only the Z is 20:20t. This after exausting 3 day calculations, belt lengths,inertia, tooth engagement, speeds, etc. and at the end -common sense.
This is a separate thread of its own. I believe this the wisest decision between speed, acceleration, precision.


2.I decided to redesign the Z as it bothered me, especially with this long 1400mm belt. At the end common sense also helped here. At the end raised a bit the overhang without compromising anything so much. I design like this-until i see perfection at every detail.

So the Z. Tried to design it like a Russian tank from WW2. All plates are 20mm Aluminum.

- it would be covered against dust from all sides



-The cheese . The additional holes at the front are for mounting extra things, like: 3D plastic head, plasma torch, engraver, light and so on. The front plate on the moving box is separated in 3 parts. The lowest one is for the case when a so high object is machined that the spindle has to be all in, hence from there access to the nut of the spindle. the second part allows exchange of the spindle. The upper one stays there forever.



-The linear movement and where is placed. I even decided against using it for the hammer. the idea of making a precision machine and the trying to brake it seems less and less attractive. So this one will make the other which will be purpose build 5-6 axis, but anyways as i have 2 ball screws i decided to fit them.



-Reinforced the motor plate, this will hold the drag chain too. The belt now is very short as i like it, no extra pulleys and 6-7 teeth engagement each ball screw pulley. So seems ok to me.






The rotating ball nut assembly. 20:30t hence 1.5:1 driven. Compromise due to common sense. At the end precision and power at the same time is the aim.

2048 encoder on the motor, so more or less 20m/min. I see on the motor specs that it can go up to 4500rpm, just the curve is straight till 3000rpm. The resolution will be ~0.003mm on all axis , 0.001mm on the Z/ 1605 screw and 2500ppr encoder/. That without any artificial gearing or micro stepping which is not needed it seems. Thats good, cause the Galil board is not micro stepping board.

[Boyan Silyavski]

Hi Silyavaski

You have been busy with CAD, nice drawings, what cad package are you using?.
And great to see you have assembled the parts and drives....
How do you intend to join all the steel sections and the vertical bracing? By welding?
-
From memory you are going to use this machine with an impact hammer to make musical instruments.
-
Will it be an air operated hammer similar to one of these? https://www.google.com.au/search?q=a...w=1215&bih=817
-
I was using a small one hand one last week to break up some concrete. they cam deliver quite a blow, You can turn them down by using both a pressure and flow regulator. the settings will depend on what sort of material you are acting upon. even at a low setting the energy released is significant.
-
Tubular steel is very strong no doubt, however it can vibrate, particularly if the hammer is set to oscillate near the resonant frequency of the frame. Without very sophisticated FEA software it is hard to conceptualise just how a structure will behave. however you may find it advantages to consider the issues involved in advance and if vibration turns out to be a problem have a means of increasing the mass of the structure and what sort of damping measures you take to reduce the amplitude to an acceptable level.
.
Here is a link to an excellent paper on concrete filled steel structures used in machine design. http://www.mech.utah.edu/~bamberg/re...e%20Design.pdf
-
Regards
John

Thanks for the link.

Here is the comparison picture with the 3.2kw spindle. It weights next to nothing, compared to the spindle, which is a monster.



here i started to put the electronics together. No power cable in front, all go back shielded by the alu plate. Later all in metal box, due to the occasional plasma jobs.






The program i use is Sketchup, cause i am very fast at it. trying to learn also a proper Cad also at the same time. /NX9/.

[TonyD]

Can't wait to see this come together, keep up the good work. :)

[JAZZCNC]

I see no point in having 2 ballscrews to drive the Z axis.? Whats the thinking behind this.
Your just making the motors work harder and increasing costs for no practicle gain.? You'd be much better spending the money on a second ballnut and creating Zero backlash.!!

[Boyan Silyavski]

I see no point in having 2 ballscrews to drive the Z axis.? Whats the thinking behind this.
Your just making the motors work harder and increasing costs for no practicle gain.? You'd be much better spending the money on a second ballnut and creating Zero backlash.!!

Hi Dean,

Yeah, what i was thinking, you got me there . I started the design half an year ago, and learned a lot during this time.The thing is that i wanted not only to have 2 ball nuts but also 2 extra ball screw supports, " 4 is better than 2 " to resist the vibration. Thats why the double ball screw. Also the double ball screw saves on the total Z length.

Now i am not so sure. Still its not too late. Now i see that i could have made the ball screw machined so that it accepts double support at the ends. I have an extra ball screw at home, longer, i mean. Then the only thing that needs changed will be to buy 2 longer Hiwin rails to compensate. Have to rethink that. There is still time.

Now going this way of thinking i start doubting if i should not make the whole z axis 100mm longer and have travel of 300mm instead of the 200mm as its now. Could just raise the vertical bars on the sides of the base with 100mm without compromising any integrity. They are ~80mm high right now. the thing is would i really need that extra 100mm and for what?

[JAZZCNC]

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.!

[John McNamara]

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.
https://www.google.com.au/#q=brinell+pitting

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.

Regards
John

[John McNamara]

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.

Regards
John