PDA

View Full Version : BUILD LOG: Aluminium profile CNC



BriceO
27-10-2017, 12:55 PM
Hi everyone,

I'm currently building a CNC router of 1.8x1.2 meter to cut wood (and probably test aluminium).
23110
I use aluminium profile 8 series and 20mm aluminium plate. 4X NEMA 23 with a 48V PSU and a gecko G540. Here is the specs of the motor: (381 oz In. Holding Torque, 2.55V Rated voltage, 3.5 Amps Current Per Phase, 0.73 ohms Resistance, Inductance 2.8 mH).

I had a proposition to use for the X and Y, 20mm lead, with a max speed of 500 IPM at an acceleration of 0.15G. For the Z, 10mm lead, with a max speed of 300 IPM at the same acceleration. My goal is to have a resolution of 0.01, an accuracy of a least 0.1mm.

I have several questions:

Is this general design seems to be ok?
Are my max speed and acceleration calculated correctly? Or should I take 20 or 10mm lead?
Is it a correct speed / acceleration for the size?
Do I need to have a ballscrew preload torque?
Is the position of the linear bearing/ballscrew good?
Which space should I have between linear block?


Thanks for your help.

Chaz
27-10-2017, 01:46 PM
I would recommend putting more strengthening between the left and right profiles that run from front to back.

The single front and rear ________ beams will only offer some rigidity. Ideally from this shape - | ____ | you want to go to something like O.

Nr1madman
27-10-2017, 06:38 PM
Hello!

Im certainly no expert but the way I see it you need to think about how you are going to fit your ballscrews..
They take more room than the linear rails offer and from what I see in the cad there are no spacers or something like that..?

Skickat från min SM-N910C via Tapatalk

Nr1madman
27-10-2017, 06:40 PM
Also on the Z axis it's stronger to build the rails on the moving plate and the bearings on the stationery side :)

Skickat från min SM-N910C via Tapatalk

routercnc
28-10-2017, 08:31 PM
One thing to watch with that design is that the gantry will need to be shimmed on one side between the gantry and side plates because you have trapped the long X axis rails between the sides of the bed. That is why most people put the rails on top of the profile as the tolerance can then be taken up by slightly over sized holes in the side mounting plate.
In other words the gantry length will have to be cut very accurately so the side plates are a snug fit into the rail carriages

BriceO
29-10-2017, 07:10 PM
Nr1madman, you're right there is a space between the linear bearing and the plate. I was thinking to add a 20mm spacer.
23115

Thanks for your advices, I will do the changes. In my actual design I have a another profile in the middle of the left and right profiles, but I will add more.
routercnc, nice idea I was thinking that I can order the profile already cutted.

Thanks everyone ;)

And what do you think about the linear bearings?

routercnc
29-10-2017, 07:35 PM
Your question about linear bearings - do you mean size? If so 20mm on all axes.
What is the plan on the Y ball screw? It goes straight through the Y and Z axis? With that type of layout some people space the YZ away from the gantry and run the ball screw behind. But this weakens it because of the overhang.
A more popular design is the L shaped gantry with the ballscrew running behind allowing the YZ to be close into the gantry.

BriceO
30-10-2017, 09:22 AM
Your question about linear bearings - do you mean size? If so 20mm on all axes.

I mean which lead should I take, 20 or 10mm lead? I calculated a max speed of 500 IPM, does it seems to be correct? And do I need to have a ballscrew preload ?


What is the plan on the Y ball screw? It goes straight through the Y and Z axis? With that type of layout some people space the YZ away from the gantry and run the ball screw behind. But this weakens it because of the overhang.
A more popular design is the L shaped gantry with the ballscrew running behind allowing the YZ to be close into the gantry.

I planned to run the ball screw behind the gantry for this axis, but you're right I'll change it for the L shaped gantry.

For the longest axis, which one is the "best" design?
Add a spacer to the ballscrew. The ballscrew runs behind the plate and this plate will be near the bearing blocks. Something like this:

23117

Nr1madman
30-10-2017, 09:49 AM
I mean which lead should I take, 20 or 10mm lead? I calculated a max speed of 500 IPM, does it seems to be correct? And do I need to have a ballscrew preload ?



I planned to run the ball screw behind the gantry for this axis, but you're right I'll change it for the L shaped gantry.

For the longest axis, which one is the "best" design?
Add a spacer to the ballscrew. The ballscrew runs behind the plate and this plate will be near the bearing blocks. Something like this:

23117Hmm don't really understand but is "lead" the same as "pitch"?
Have read a lot about lead on the zone but that seems to talk about trapezoidal screws and not ballscrews?
Anyway what do you want to cut and in what resolution?

If you plan on having the ballscrew on the outside of the plate as in the picture then please don't forget that the screw must be longer then the calculated travel as the plate will travel inside the bearings :)

Skickat från min SM-N910C via Tapatalk

BriceO
30-10-2017, 10:21 AM
Hmm don't really understand but is "lead" the same as "pitch"?

Yes, exactly I mean pitch. I would like to cut mainly wood and a few tests with aluminium.

My goal is to have a resolution of 0.01 and an accuracy of 0.1mm. I tried to calculate the speed with a hiwin 2020 ballscrew, KL23H2100-35-4B NEMA23 and found a max speed of 500 IPM. Is it possible?

Here is the specs of the motors (4X):
23119

routercnc
30-10-2017, 07:30 PM
Ok thought you meant the linear bearings on the rails

For ballscrews my machine is 5mm pitch all round but if I was starting again then 5mm Z and 10 mm for X and Y. This gives better rapids in wood and should be Ok for aluminium but if you drive the X and Y via belt and pulley you can swap out the ratio on X and Y to give 2:1 to give more torque (and less speed) if needed on the aluminium
Not sure about 20 mm pitch - will give very high rapids but you loose some torque and could stall the steppers? Anyone tried this much pitch? May be ok with enough voltage on the steppers . . .

BriceO
31-10-2017, 08:21 AM
Not sure about 20 mm pitch too :) Belt and pulley can offer more possibilities, good idea! Do you know where I could find good ones?

Someone made a graph for me for the same motor with different pitch considering the weight of the gantry, ballscrew type, motors specs,... :
23121

10mm seems to be a good compromise. What do you think about that?

Nr1madman
31-10-2017, 08:31 AM
I think 10mm pitch will be plenty good :)
Atleast I hope so as I have it on my machine that I'm building!

Seems like you chose good motors but if speed is important to you they will perform much better with higher voltage psu and drivers. The G540 is a bit outdated I think :)
If you have already bought it its okey because it probably offers good stable motion. But you can get better performance!

Skickat från min SM-N910C via Tapatalk

BriceO
01-11-2017, 08:23 PM
Ok, I took a quick look a your CNC, it's a nice work Nr1madman! It seems to be finished soon :)

I can't figure out why is it better to build the rails on the moving plate and the bearings on the stationery side. Maybe someone could explain me.
And is it necessary to have ballscrew with preload torque?

I already bought the G540 for my 1st machine but I really like it, it just works fine.

I'm finishing to update my design and will probably order linear rail Hiwin HG20 (1800,1380,300mm) and ballscrews RM2010(1795,1375,295mm).

Really excited to start to build it!

Nr1madman
01-11-2017, 09:08 PM
The reason to mount the rails on the Z axis plate is part that the rails actually strengthens the plate. And if you have the bearings on the plate you always have the same distans (leverage) from bearing to the tool tip. If you have the rails on the plate you can raise the part that you are machining closer to the spindle and shorten the distance from bearing to tool tip for higher rigidity.

Most people seem to buy standard ballnuts without preload. What I've seen some people do is use 2 ballnuts and preloaded these against each other for backlash free operation. Or are you talking about ballscrew mounting with 2 fixed bearings instead of a floating bearing in one end?

Skickat från min SM-N910C via Tapatalk

routercnc
01-11-2017, 09:11 PM
Z axis bearing arrangement
Arrangement A: With rails on the moving plate (Z axis) the lower bearing is always as close as possible to end of the tool.

Arrangement B: With rails on the stationary plate (Y axis) the lower bearing is much further away from the end of the tool (vs arrangement A) when cutting close to the home position / tall parts. This is less stiff an arrangement Vs arrangement A. However, when cutting at full stretch near the table than they are the same.

So sometimes they are the same, and sometimes A wins in terms of stiffness, depending on the height of the part you are machining.

I've seen arguments made that arrangement B is OK, probably on small Z travel machines, and that it could be said to be a bit easier to build. Jazzcnc put forward an argument for B, can't remember what it was now. My personal preference is A.

Ballscrew 'preload'

"Ballscrews with preload torque" ? You put this right after the sentence over rails and bearings so assume you mean preload on the bearing carriage- the part which slides on the rail? If so ZA is better than Z0 if you have the choice:
http://www.mycncuk.com/threads/9373-profiled-rail-wich-preload-do-you-use-ZO-%28light%29-ZA-%28Medium%29-for-a-diy-router

If you mean preload on the ballscrew - the part which rotates and drives the axis then for general DIY machine the ball nuts as supplied from China are fine. They typically have 30 - 50 um (0.03 - 0.05 mm) backlash. C7 grade is fine for DIY machine, but if you really want there is a C5 grade:
http://www.mycncuk.com/threads/1558-Ball-Screw-Accuracy-V-Price

Nr1madman
01-11-2017, 09:14 PM
Oh!
Don't think you need 2010 screw for Z axis.. 1605 should be fine. Might even be okey with 1204 for Z if you have a smart mounting strategy :)

Have you calculated the length of the ballscrews from desired ballnut travel + ballnut distance + end machining or from what is easy to mount in your design?

Skickat från min SM-N910C via Tapatalk

Nr1madman
01-11-2017, 09:18 PM
@routercnc
I should just shut up, you explain so much better :D

Skickat från min SM-N910C via Tapatalk

BriceO
08-11-2017, 02:32 PM
Thanks guys for the explanations ! :) I'll probably use arrangement A and 1605 for the Z axis.
I have 6082 T651 aluminium plate, do you think is it flat enough to use it?

Chaz
08-11-2017, 02:54 PM
Thanks guys for the explanations ! :) I'll probably use arrangement A and 1605 for the Z axis.
I have 6082 T651 aluminium plate, do you think is it flat enough to use it?

Nope, try get tooling plate. www.clickmetal.co.uk

BriceO
08-11-2017, 04:03 PM
Sadly, I live in Switzerland. Is "tooling plate" a specific type of aluminium as T6 ?

Chaz
08-11-2017, 04:05 PM
Sadly, I live in Switzerland. Is "tooling plate" a specific type of aluminium as T6 ?

No, its a milled / ground flat version. Its made in Europe and must be commonly sold. I did see the manufacturer name at a point. Something like Gecia or similar, dont remember.

Nr1madman
08-11-2017, 06:58 PM
It's also possible to use "eco cast" and similar flat stock. I looked at this from aluminiumwarehouse as they send over Europe. Im in Sweden so similar problem.

I think toolingplate is called mic6 sometimes to but I might be wrong on this one..

Skickat från min SM-N910C via Tapatalk

BriceO
08-11-2017, 08:32 PM
Thanks, I just find another site just in case it can help someone: zappautomation but I will try to find it locally.
I understand why the mic-6 would definitely be beneficial in the carriage, where the rails bolt directly, so you only need to worry about alignment. I was just asking me if it is as important as that concerning only the side plates? I ask that because I have a plate that I could use.

routercnc
08-11-2017, 09:31 PM
Whether you can use the plate you already have for the gantry sides really depends on how flat and straight it is. If it is not flat enough you will put some kind of loading in the X axis carriages and they may bind or at least have a shorter life.

If you have the plate already then try lightly clamping it in place and see if the carriages move freely. Maybe you can get away with a bit of shimming.

Ideally I would go for the tooling plate myself as it is not much more than the regular plate and is much, much flatter.

One of the earlier questions was 'is tooling plate a type of T6?'. My understanding of the types aluminium goes as follows-

Aluminium 1000 grade (1xxx)
This is good for bending into shapes and is usually what the thin stuff if made from. But it is a fairly pure aluminium (99.5%) and likes to weld itself to the cutter, so flood or heavy spray coolant is required. Plus I have been recommended by experienced machinists to use carbide cutters.

Aluminium 6000 grade (6xxx)
This good for machining, and is what the general purpose thicker stuff is made from. It is only 97.9% aluminium with the rest coming from various beneficial ingredients.
Of the 6000 series you will often see 6061, which is a specific and popular product from that range.
Of the 6000 series (and maybe others as well?), -T6 (e.g. 6061-T6) refers to the product being heat treated and aged, which improves the material properties. Again this is a popular choice.

There are other grades, 2000, 3000, 4000, 5000 (good for corrosion e.g. marine use), 7000 (stronger), 8000. I've not knowingly used these other grades and have certainly not ordered them for workshop use.

Eco-cast / tooling plate / mic-6
Happy to be corrected but tooling plate / ecocast / mic-6 are the same basic thing to my mind - machined fairly flat and good to use as-is for DIY CNC machine.

So in short, for main construction go for 6061-T6 to get the machinability and other properties you need, and where flatness is important go for the ecocast/tooling plate/mic-6 versions of this grade which have been machined flat for you.

Hope this helps, and if anyone can add to this or correct me etc. please do.


p.s. Having a peak at Wikipedia to see what they say about it all gives a whole lot more info and here is the link if you are brave enough:
https://en.wikipedia.org/wiki/Aluminium_alloy

BriceO
16-11-2017, 09:52 PM
Hi,

It's clearer now, really nice! I finally found locally a plate 20mm, but this is grade 5083. (500x500mm is 182.- with the cut.)
Here is the specs: height tolerance: +/-0,1 mm, flatness tolerance max. 0,15 mm/m

I have made several changes on my design according to your advice. I'm trying to find the best way to mount the rails.
23212

In this configuration, the block is on top of the extrusion. Will it be stiffer?

23213
In this arrangement, it will be easier to mount as the space between the block and the plate is the same size as my aluminium height (20mm).

Which one do you think is the best? (The first image has the y axis a little bit lower)

Thanks again for your help :)

Nr1madman
17-11-2017, 07:50 AM
In both scenarios you need a way to adjust the width of the gantry as you will be "trapping" either the ballnut or both ballnut and linear bearings.

If you have the rail on top it can be adjusted sideways in the screwdown moment.

For the ballnut you can mount it like that if you shim it..

Skickat från min SM-G955F via Tapatalk

routercnc
19-11-2017, 08:21 PM
Top one will most likely be stiffer as you are not bending the gantry sides. Limiting factor is the gauge of the extrusions on the bed sides. If space and access to the bed at each end allows you can plate over the ends to join them to each other.

BriceO
20-11-2017, 09:47 AM
I'll go for the top one so, I wasn't thinking that it could have any bending problem, thanks.


Limiting factor is the gauge of the extrusions on the bed sides.
I'm not sure to understand it. Do you mean the extrusion is it too high?

Good idea for the end plat, do you think 5mm aluminium is enough to do it?

I found this documentation about hiwin rails : http://www.hiwin.com/pdf/linear_guideways.pdf
It can be interesting for someone. Is it a good choice to have a HGW (wide flange carriage) could be a good choice for the Y axis for example? And HGH for X and Z axis.

Any advice higly appreciated.

routercnc
20-11-2017, 01:26 PM
I'll go for the top one so, I wasn't thinking that it could have any bending problem, thanks.


I'm not sure to understand it. Do you mean the extrusion is it too high?

Good idea for the end plat, do you think 5mm aluminium is enough to do it?

I found this documentation about hiwin rails : http://www.hiwin.com/pdf/linear_guideways.pdf
It can be interesting for someone. Is it a good choice to have a HGW (wide flange carriage) could be a good choice for the Y axis for example? And HGH for X and Z axis.

Any advice higly appreciated.

The extrusion is not too high all I wanted to point out was that using extrusion, especially thin wall (gauge) extrusion, will be the limiting factor for the stiffness. The wall is thin, and it essentially has lots of deep slots cut in it. Imagine pressing sideways where the gantry rail is situated, and imagine how it will want to bend and vibrate.

Lost of people use steel box section instead as it is much stiffer, with a continuous outer section, usually with a high wall thickness (to allow thread tapping), and it is cheaper.

End plates of 5mm will be fine as shear panels don't need to be massively thick to be effective, but it will limit feed in / out access if that is a consideration.

Hiwin carriages - either wide or narrow are both fine. Use wide if that gives a better footprint and mounting for your design.

BriceO
20-11-2017, 02:46 PM
Thanks, is it the same problem for the Y axis? :suspicion: Should I place the rails on top and bottom or is it fine?

To be honest, I can't really imagine how it will bend and vibrate. I was thinking that the weight/force is supported by all the length of the extrusion.

Davek0974
20-11-2017, 03:05 PM
Thanks, is it the same problem for the Y axis? :suspicion: Should I place the rails on top and bottom or is it fine?

To be honest, I can't really imagine how it will bend and vibrate. I was thinking that the weight/force is supported by all the length of the extrusion.

Yes it is, but, the ends are fixed - the weight/force now tries to act upon the whole beam but cannot move the ends as they are fixed - it will then act upon the point where the force is applied, if say it is applied centrally then the force will try and bend or push the beam in the opposite direction to the force - the beam will bend. The skill in designing beams is to transmit those forces to the ends of the beam without letting it bend - this is done by using heavy enough section material or bracing thinner section material with struts or triangular trusses.

Vibration is the same really, just many more, smaller forces that need dampening out or preventing in the first place - mass is a good way of stopping vibration or at least moving the harmonic point to somewhere outside the range of expected vibrations.

BriceO
21-11-2017, 10:16 AM
Thanks for these explanations, I used the Item site to calculate deflection of the profile (http://product.item24.co.uk/en/home/products/product-catalogue/productdetails/products/construction-profiles-8/profile-8-120x80-light-natural-41665.html) for 1200mm and 400N. If I do it right I have a deflection of ~0.01 mm.
I was thinking that Aluminium was a good compromise between weight/strength and offer a good flatness. I don't have enough experience to determine how bad is it.

Sadly, I already have these "light" profiles. Should I go for steel box section instead for X and Y? Do you have any advice plz?

routercnc
21-11-2017, 01:28 PM
Thanks for these explanations, I used the Item site to calculate deflection of the profile (http://product.item24.co.uk/en/home/products/product-catalogue/productdetails/products/construction-profiles-8/profile-8-120x80-light-natural-41665.html) for 1200mm and 400N. If I do it right I have a deflection of ~0.01 mm.
I was thinking that Aluminium was a good compromise between weight/strength and offer a good flatness. I don't have enough experience to determine how bad is it.

Sadly, I already have these "light" profiles. Should I go for steel box section instead for X and Y? Do you have any advice plz?

The deflection calculation will probably be just simple bending, so either simulates a plunge in Z or simulates the sag caused by the weight of the spindle assembly. This is usually easy to get a low value.
What really tests the machine design is cutting in the X direction (confusingly many US builders call this the Y direction, so be aware if you are reading different forums) because this puts a moment on the gantry and tries to twist it. This is usually the limiting factor and will result in much more deflection at the tool tip than the Z direction loading.

However, based on the fact you have the extrusions already, and you mainly want to cut wood, then stay with them and build it as per the top picture in post #26.

Also be aware that the aluminium profile is not especially flat unless you have it specially machined.

BriceO
24-11-2017, 10:19 AM
Ok, I will do the best with this and maybe add steel plate to the back to add weight and strength.

I just received an offer from Chai for these components:

-2 HIWIN HG20 rails + 4 blocks hgh20CA ZA 1800mm
-2 HIWIN HG20 rails + 4 blocks hgh20CA ZA 1380mm
-2 C7 Ball screw RM2010 total length end machined 1760mm with ballnut
-1 C7 Ball screw RM2010 total length end machcined 1360mm with ballnut
-3 2010 Nut Housing
-3 Jaw Flexible Coupling 6.35mm*12mm (Ballscrew to NEMA23)
-3 BK15/BF15 P5 AC

Chai price is 656 usd Total. Air shipping cost is included.
Fred from BST Automation is USD1155.00 for the same items.

Is it normal to have a big difference?

Davek0974
24-11-2017, 10:39 AM
656usd is amazing!

Nr1madman
24-11-2017, 01:37 PM
656usd is amazing!I agree.. take it before he finds out that he calculated wrong :D

Just a reflection.. with that long ballscrews and direct couplings the motors will stick out in the back/front where you have mounted them.
Have you thought about using pulleys or shorter ballscrews?

Skickat från min SM-G955F via Tapatalk

BriceO
24-11-2017, 02:19 PM
656usd is amazing!
It seems a very good price to me too :)

Nr1madman, yes I plan to have motors on front of the cnc. I would like to have the maximum length. I could have miss something, is there any advantage to use pulleys?

Nr1madman
24-11-2017, 05:56 PM
It seems a very good price to me too :)

Nr1madman, yes I plan to have motors on front of the cnc. I would like to have the maximum length. I could have miss something, is there any advantage to use pulleys?For me with limited space a pulley system is good because you can fold the motor into the machine area so that it doesn't stick out.
Also it's said that the belt in a pulley system helps with resonances. Of course you need good pulleys without backlash like htd:)

Skickat från min SM-G955F via Tapatalk

Davek0974
25-11-2017, 09:23 AM
Yes, resonance is better with pulleys in there, you can also easily tune/change the ratio for speed tuning.

mekanik
25-11-2017, 09:56 AM
Hi Brice0
Could you post a link to Chai's store.
Regards
Mike

BriceO
25-11-2017, 03:04 PM
Here is the actual design
23256

But I will add pulleys as you recommend, I could probably keep the same length to add pulley?
I was thinking to add something similar to the design of JoeHarris:
23255

Hi mekanik, here is the link of Chai Store: www.ebay.fr/usr/linearmotionbearings2008