PDA

View Full Version : BUILD LOG: Gantry Aluminium thickness guidance



dachopper
05-12-2016, 03:33 PM
Hi guys,

I have started acquiring components for a 1500x800x200 build area gantry style router, and still am undecided about the gantry end plate / x axis and z axis plate thickness required or recommended

I have seen some commercial hobby components as thin as 6mm aluminium for end plates, and read others recommending 15/16 minimum, or 20mm.

My Z height calls for an end piece of about 300 x 440 high. the X design has 2 x 80 x 80 T slot mounted with a 80mm gap for the X motor and ballscrew in the middle, then a 170 gap below to the mount plate on the Y axis



Can anyone give some advice on what happens if it's too thin, and what would work.

If guys use 20mm for the end plates, what do they use for the x axis and z axis plates?


All advice appreciated
Nick

dachopper
06-12-2016, 06:57 AM
Hi guys,

I have started acquiring components for a 1500x800x200 build area gantry style router, and still am undecided about the gantry end plate / x axis and z axis plate thickness required or recommended

I have seen some commercial hobby components as thin as 6mm aluminium for end plates, and read others recommending 15/16 minimum, or 20mm.

My Z height calls for an end piece of about 300 x 440 high. the X design has 2 x 80 x 80 T slot mounted with a 80mm gap for the X motor and ballscrew in the middle, then a 170 gap below to the mount plate on the Y axis



Can anyone give some advice on what happens if it's too thin, and what would work.

If guys use 20mm for the end plates, what do they use for the x axis and z axis plates?


All advice appreciated
Nick


60 views and no advice, someone must have an idea

njhussey
06-12-2016, 10:23 AM
Hi Nick,

Welcome to the forum :encouragement: don't get hung up on views and no replies...it's hard to give a meaningful reply without knowing a bit more so most people will shy away from giving advice. It's a bit like saying I've a room to paint, how much paint do I need? Have you got a cad drawing of your router we can look at? What are you aiming to cut, how long is your Z axis etc. etc. etc. The strength/thickness needed will depend a lot on your design and what you're looking to cut, give us some more to go on and we'll help you out.

Robin Hewitt
06-12-2016, 12:17 PM
End plates for a gantry? So what happens when you accelerate the head hard along the gantry or the tool plunges in to the side of something resilient? That is the moment you realise that a plate simply does not cut the mustard and you really needed to think in triangles.

dachopper
06-12-2016, 01:07 PM
End plates for a gantry? So what happens when you accelerate the head hard along the gantry or the tool plunges in to the side of something resilient? That is the moment you realise that a plate simply does not cut the mustard and you really needed to think in triangles.

Well, the Nema 23 will probably stall if all of the end stops fail. Chances of that happening......

What happens if I'm using a tube design with thin walls and the plate rams the thin skinned tube?

Here is the basic design.

The Y extrusion is quite big, 80x160, and the others are all 80/80 profile.

This is the rough plan
19820
This is where I'm up to
1982119822


To be used for 3d Printing, Composite 3d milling, wood, and possibly aluminum

njhussey
06-12-2016, 03:44 PM
Well, the Nema 23 will probably stall if all of the end stops fail. Chances of that happening......

Greater than you think....well if your home switch becomes loose from vibrations (fast trochoidal milling) so your gantry slams on a rapid home into the side beams.....luckily the AM882's have stall detect!!


What happens if I'm using a tube design with thin walls and the plate rams the thin skinned tube?

Guess it'll bend it!


Here is the basic design.

The Y extrusion is quite big, 80x160, and the others are all 80/80 profile.

This is the rough plan
19820
This is where I'm up to
1982119822


To be used for 3d Printing, Composite 3d milling, wood, and possibly aluminum

Somewhere on the forum there is a bending moment calculator which will sort this for you, however I'd say minimum of 15mm for the plates, and for the difference in cost go 20mm, and I'd strongly consider putting a plate across your two 80*80 Z axis extrusions to stiffen up the gantry.

for the Z axis I'd put thicker plates on as those don't look that thick and I'd put the rails on the front plate not back to stiffen it up. I'd also consider connecting your motors to the ballscrews via belts and pulleys rather than directly, this helps take out any resonance (from cutting) and stops it being fed back to the stepper motors.

If you're using the ballnut housing that's in picture 2 how are you going to connect it to your Y axis plates, you'll not get to the screws behind it to tighten it?

MikeyC38
06-12-2016, 06:19 PM
Hi Nick

As others have said, you do need to be more specific which you have done by showing details of your build and what you intend to cut. Rigidity is your best friend for any cnc build and as others have said plates across the end of the long axis will stiffen the frame significantly. In my build here (http://www.mycncuk.com/threads/8206-Ar-last%21%21%21-Started-my-Gantry-3-Axis-CNC-Build) I used 80 x 40 heavy gauge extrusions ( 4kgm+) with 15mm 6082 T6 plates either end. The gantry sides are 20mm 6082 T6 water jet cut with heavy gauge 80 x 40 extrusion for the (short) y-axis. I am very pleased with the overall rigidity but will reserve judgement until I do my first cuts on metal. It might appear over engineered but I took the advice offered on the forum and I'm confident the machine will deliver the levels of accuracy I need. The use case for my machine is cutting balsa, hardwoods and aluminium at reasonable speeds, hence the robustness of the construction for the most difficult use case (cutting aluminium).

Hope this helps

Mike

JAZZCNC
06-12-2016, 07:33 PM
End plates for a gantry? So what happens when you accelerate the head hard along the gantry or the tool plunges in to the side of something resilient? That is the moment you realise that a plate simply does not cut the mustard and you really needed to think in triangles.

Another really helpful comprehensive post robin from your Vast experience.!! . . . . Why don't you just shut up if can't give relevent and helpful comments.

You didn't even think to ask about Style of router and what his uses for it where.! . . . The design he's using will work fine for his needs and his question for plate thickness is perfectly valid with this design.! . . . He didn't need sarcastic pointless reply about triangles when all he asked was for plate thickness for Gantry sides.:thumbdown:


60 views and no advice, someone must have an idea

It's long way to OZ there's time delay.!!!

I build similair design and depending on the Gantry side heights either 15 or 20mm will work. The Red machine uses 15mm sides but as lower sides. White one uses 20mm.
Like wise the Red machines uses Z axis with Rails on the front plates like has been suggested. However the White one is the other way around.?

Reason for this is down to usage. The red machine was designed just to cut thinner material upto 75mm. It will happily cut upto aluminium.
The white machine had requirement to cut deep material with long tools in Clay model board which isn't very hard material. This required the spindle lifting higher to allow for long tool hence rails on back plate.
Both machines will happily cut aluminium with light cuts, infact the very first Job the customer cut was 4 x aluminium plates for where the machine fastens to the base frame which you can just see on one of pics where machine meets frame.(I only supplied the machine)

Me personaly I would use 20mm every where, even Z axis. Also with Z axis if don't need long tools or deep cuts then would always go with rails on front plate.

Regards the frame and gantry then I'd consider a few bracing plates like been suggested. . . . Hey maybe even cut them in triangle shape.!!

With little bit of bracing then this design will easily do everything you asked about. Aluminium work will require lighter DOC cuts but will still handle it no problem.

Good luck and keep it up.

routercnc
06-12-2016, 07:46 PM
I'm glad I waited for the design sketches as I mis-understood your question in the first post, now it is clearer.

Gantry end plates at least 15mm, more like 20mm to give yourself a chance with the aluminium machining. 1500x800mm is a large machine and stiffness drops considerably as you go bigger. Really I would recommend raised X axis designs for aluminium but you here now so need to recover what you can.

Long axis (I would call it X) end plates are to stop the machine ploughing off the end of the rails but you'd be surprised how powerful the steppers as when driven through the force multiplying effect of the ballscrew. You could sit on the gantry for example and it would move you around without a problem.
I would not go for 6mm end plates, but 10-15mm as a guide. Final decision would most likely be decided on if you can cut them out of an offcut plate used elsewhere as they would be quite small. The other thing to consider is they normally double up as stepper motor mounts for the X ballscrews so that will also drive the thickness.

Z axis and Y axis plates would go for 20mm personally.

dachopper
07-12-2016, 12:05 PM
Greater than you think....well if your home switch becomes loose from vibrations (fast trochoidal milling) so your gantry slams on a rapid home into the side beams.....luckily the AM882's have stall detect!!



Guess it'll bend it!



Somewhere on the forum there is a bending moment calculator which will sort this for you, however I'd say minimum of 15mm for the plates, and for the difference in cost go 20mm, and I'd strongly consider putting a plate across your two 80*80 Z axis extrusions to stiffen up the gantry.

for the Z axis I'd put thicker plates on as those don't look that thick and I'd put the rails on the front plate not back to stiffen it up. I'd also consider connecting your motors to the ballscrews via belts and pulleys rather than directly, this helps take out any resonance (from cutting) and stops it being fed back to the stepper motors.

If you're using the ballnut housing that's in picture 2 how are you going to connect it to your Y axis plates, you'll not get to the screws behind it to tighten it?

Good point - any tips?

I can do it up before installing, but that will be loaded with alignment danger

I could install a horizontal shelf over the top of it, rotate the flat face 90 so it points up, and do it up from the top instead of on the side?

dachopper
07-12-2016, 12:10 PM
Hi Nick

As others have said, you do need to be more specific which you have done by showing details of your build and what you intend to cut. Rigidity is your best friend for any cnc build and as others have said plates across the end of the long axis will stiffen the frame significantly. In my build here (http://www.mycncuk.com/threads/8206-Ar-last%21%21%21-Started-my-Gantry-3-Axis-CNC-Build) I used 80 x 40 heavy gauge extrusions ( 4kgm+) with 15mm 6082 T6 plates either end. The gantry sides are 20mm 6082 T6 water jet cut with heavy gauge 80 x 40 extrusion for the (short) y-axis. I am very pleased with the overall rigidity but will reserve judgement until I do my first cuts on metal. It might appear over engineered but I took the advice offered on the forum and I'm confident the machine will deliver the levels of accuracy I need. The use case for my machine is cutting balsa, hardwoods and aluminium at reasonable speeds, hence the robustness of the construction for the most difficult use case (cutting aluminium).

Hope this helps

Mike

Thanks mike - 1 question,

Your gantry sides are 20mm - these are the largest plate connecting the Y and X axis, where did you use the 15mm plate for?

Any did you use plate for the Z / X axis.

I have also used high grade extrusion, the bare weight of the aluminium along for me was 76 kg. I think the Y axis was 9 kg/m, and the X axis around 5-6.

MikeyC38
07-12-2016, 01:54 PM
Thanks mike - 1 question,

Your gantry sides are 20mm - these are the largest plate connecting the Y and X axis, where did you use the 15mm plate for?

Any did you use plate for the Z / X axis.

I have also used high grade extrusion, the bare weight of the aluminium along for me was 76 kg. I think the Y axis was 9 kg/m, and the X axis around 5-6.

Hi Nick

I used 15mm plate at either end of the long extrusions (x-axis) (see my build log photos for the bed construction). For the Z axis construction I used 20mm 5083 cast and machined toolplate. It has a very fine and accurate surface finish which is critical for the setup and accuracy of that axis.

Regards
Mike

dachopper
07-12-2016, 01:59 PM
Hi Nick

I used 15mm plate at either end of the long extrusions (x-axis) (see my build log photos for the bed construction). For the Z axis construction I used 20mm 5083 cast and machined toolplate. It has a very fine and accurate surface finish which is critical for the setup and accuracy of that axis.

Regards
Mike

I'm trying to CAD up another concept, but Fusion360 is down on my laptop !

njhussey
07-12-2016, 02:21 PM
Good point - any tips?

I can do it up before installing, but that will be loaded with alignment danger

I could install a horizontal shelf over the top of it, rotate the flat face 90 so it points up, and do it up from the top instead of on the side?

I did the same as you, only I'd built it hence how I know!! I bought two of these (http://www.zappautomation.co.uk/mechanical-products/ball-nut-brackets/mgd16-ballnut-bracket.html) style for mine and they're great.

dachopper
08-12-2016, 12:55 AM
44 Pounds !!!!!!!!!!!!!!!!!!!!!!!!!!!! wtf, is that hand cnc'd or something !

I think I will make a horizontal plate, that protrudes over the top of the housing, and just rotate it 90 degrees, bolt from above.

I have spare 13mm plate around, so job done

njhussey
08-12-2016, 01:55 AM
44 Pounds !!!!!!!!!!!!!!!!!!!!!!!!!!!! wtf, is that hand cnc'd or something !

I think I will make a horizontal plate, that protrudes over the top of the housing, and just rotate it 90 degrees, bolt from above.

I have spare 13mm plate around, so job done
I did say that style....you can get them much cheaper if you buy the Chinese made ones on eBay or Aliexpress...:)

Sent from my HUAWEI VNS-L31 using Tapatalk

dachopper
13-12-2016, 01:08 AM
Ok guys - here is my final design

20mm thick

May put gussets over the ballscrew attachment, but Ill wait and see how rigid it is without

Nick

19987
19988

dachopper
31-12-2016, 01:21 PM
So it was a busy Christmass

Went with 20mm thick

What do you think?

20133

MikeyC38
31-12-2016, 07:36 PM
So it was a busy Christmass

Went with 20mm thick

What do you think?

20133

Hi Nick
You have been busy! so have I, finally got my machine cutting. Anyway the 20mm plate on the gantry sides will give stiffness in the Y/Z plane. BTW I noticed on your Z-axis plate the bolts are raised. You should counter bore these so that the trucks for your Z axis will have some where to be located. Remember Jazz's comments about mounting the rails on the back of the plate which holds the spindle and the trucks and ballscrew get fitted to the plate as shown in your photo.

All the best and have a successfull 2017!

Regards
Mike

dachopper
01-01-2017, 04:07 AM
Hi Nick
You have been busy! so have I, finally got my machine cutting. Anyway the 20mm plate on the gantry sides will give stiffness in the Y/Z plane. BTW I noticed on your Z-axis plate the bolts are raised. You should counter bore these so that the trucks for your Z axis will have some where to be located. Remember Jazz's comments about mounting the rails on the back of the plate which holds the spindle and the trucks and ballscrew get fitted to the plate as shown in your photo.

All the best and have a successfull 2017!

Regards
Mike

Yeah, thanks for that, I realized this as I was staring at it yesterday, will have to counter bore to even get cart to slide past the bolt head I think.

I've decided to go the other route and mount the rail on the sides of the plate pictured, and just have the cart on the back of the spindle.

JAZZCNC
01-01-2017, 11:43 AM
I've decided to go the other route and mount the rail on the sides of the plate pictured, and just have the cart on the back of the spindle.

If you don't have need for tall material or long tools then wouldn't go that route as your losing stiffness for no reason. It's not more difficult building it the other way around.

Also have you realised that you'll need to space the rails off the plate or machine channel down centre to allow clearence for the ballscrew/bearings.?
Best if you take little from each plate depending on the ball nut mount the total need machining off is the distance from bearing face to ballscrew flat which is 45mm. Profiled rail and bearings total aprox 30mm depending on make, (Hi-Win HGH-20CA are 30mm) so I'll let you do the math.?
How you devide it upto you, I just split it in half.

20134

dachopper
01-01-2017, 12:33 PM
If you don't have need for tall material or long tools then wouldn't go that route as your losing stiffness for no reason. It's not more difficult building it the other way around.

Also have you realised that you'll need to space the rails off the plate or machine channel down centre to allow clearence for the ballscrew/bearings.?
Best if you take little from each plate depending on the ball nut mount the total need machining off is the distance from bearing face to ballscrew flat which is 45mm. Profiled rail and bearings total aprox 30mm depending on make, (Hi-Win HGH-20CA are 30mm) so I'll let you do the math.?
How you devide it upto you, I just split it in half.

20134

I'm planning on using up to 200 mm z height, so really needed a design that maximizes this, when I put the first plate with back to back bearing blocks, it becomes hard to do them up ( I have to offset them , in gives less stiffness, down I loose z clearance, and up I have a greater z overhang for the same clearance. I can always bolt angle onto the spindle plate sides if on the future there is some play going on.

My plan is for the rails to be mounted flat on the back plate, I will add 15 mm spacers between the bearing block and the spindle plate to get the extra clearance as at the moment making a rail spacer, or counter sinking is far more work.

JAZZCNC
01-01-2017, 12:50 PM
If you rush and make bodge of the Z axis you'll regret it. Z axis is THE most important part of machine get this wrong and you'll always have poor finish and excess tool wear.

The extra time taken to Mill slot, even with hand router will be worth it. It's the little details that are easy to skip that bite you in the arse later.!!

Robin Hewitt
01-01-2017, 01:26 PM
I'm planning on using up to 200 mm z height

Is that scratching the top of something 200mm tall, or 200mm long cutters?

There is a big difference in the designs :chuncky:

dachopper
02-01-2017, 04:22 AM
If you rush and make bodge of the Z axis you'll regret it. Z axis is THE most important part of machine get this wrong and you'll always have poor finish and excess tool wear.

The extra time taken to Mill slot, even with hand router will be worth it. It's the little details that are easy to skip that bite you in the arse later.!!

If I mill out 15mm ( 7.5mm from each plate ) that's almost half the thickness of the plate. Surely that is going to weaken the plate sufficiently to cause me more grief, than keeping the plate stiffer and using a spacer to create the clearance.

What is the draw back of using spacers?

Yeah - we need to fit in work pieces up to 200mm high - that is not aluminium, that would be softer material like surfboard or denser foam for shaping.

Making a 1 machine fits all - because my work pieces are generally long, it's the most economical approach and I don't have room for 3 different machines when the mahority of the cutting is foam / fiberglass/carbon/ wood, 3d Printing and the odd smaller aluminium job possibly.


Regarding the z height , I have an area 80mm high to insert a bed, and fit the spindle, and then 200mm of clearance to the bottom of the gantry. I wasn't sure about the spindle overhang, so I assumed it was going to be 40-60mm, but I also made the spindle mount adjustable so If the bed takes up more room, I can raise the spindle by up to another 8 cm if I have some crazy length tool on the end. It will only be a factor for the foam jobs If I have a 200mm thick slab that needs shaping. for the most part, when working on the smaller pieces, I can attach something on the bed to raise the workpiece so the spindle is level X axis, and therefore less tourqe and vibration.

Neale
02-01-2017, 11:04 AM
If I mill out 15mm ( 7.5mm from each plate ) that's almost half the thickness of the plate. Surely that is going to weaken the plate sufficiently to cause me more grief, than keeping the plate stiffer and using a spacer to create the clearance.


It's a well-established technique, though! Look at it another way, it's less than half plate thickness and along an axis where there is little bending load, and where at least part of the channel is spanned and reinforced by the spindle mount. It keeps the spindle axis as close as possible to the Y rails to reduce leverage compared to using spacers. Probably won't matter too much for light cutting loads like foam but it seems like a good idea if you have the facilities to do it (and plenty of people have ploughed this kind of channel with a portable router, well-clamped guides, and a bit of care).

dachopper
02-01-2017, 02:05 PM
It's a well-established technique, though! Look at it another way, it's less than half plate thickness and along an axis where there is little bending load, and where at least part of the channel is spanned and reinforced by the spindle mount. It keeps the spindle axis as close as possible to the Y rails to reduce leverage compared to using spacers. Probably won't matter too much for light cutting loads like foam but it seems like a good idea if you have the facilities to do it (and plenty of people have ploughed this kind of channel with a portable router, well-clamped guides, and a bit of care).

I see your point, it doesn't really need to be exact, just enough to avoid screw contact.

Tom J
02-01-2017, 09:26 PM
Nick
I would not use anything less than 20mm, 25mm for Z plate and at least 20mm for spindle if braced by spindle bracket or other form.
If you are not limited with machining process and time than do not cut the corners - do it properly.
See how I keep changing design
2015220153201542015520156

2015720158201592016020161

after 2 days of scratching my head - still not happpy
All those changes were made to short the overhang by less than 50mm - is it worth it?

dachopper
07-01-2017, 05:28 AM
Lots of drilling and tapping yesterday,

And I had an accident and slid a bearing cart off the linear rail - then 10 bearings fell out..took ages to pack them back in there, but much easier than repacking ballscrews !

Slides well, next to attach the Y axis ballscrews, and machine the Z axis plate :)

Nick


20274

dachopper
14-01-2017, 05:03 PM
20354

more progress

dachopper
18-04-2017, 08:35 PM
Take 2,

I'm still not happy about having to put all this stuff on the k2 relay, but I can't seem to figure out any other easy way.

21419