CNC router build

[ericks]

If your machine is similar to the one in the pictures than your problem is not the pillow blocks, unless you have some with manufacturing issues or badly aligned. The problem is most probably the fact that it is a moving gantry design. I am using similar supported round rods with open end pillow blocks and have absolutely no problems at all, get very high speed and accuracy and very happy with it. The big difference is that I decided to build a fixed gantry, moving table type of machine, not what is most popular, the moving gantry type, which is more difficult to align, difficult to get the speed and accuracy right and is easy to get gantry vibrations and misalignment with.



The above parts list is fine, with a few exceptions.

Don't use ANY unsupported round rods (items 6 and 11). Why do you think that 25mm unsupported round shafts will be better than 16mm supported ones? They are NOT better.
What is the item 8 exactly do and where is it located? I don't understand that and the purpose of it.

Consider moving table fixed gantry design, and also remember that slaved motors can be a problem as well, they might cause the same sort of issue with accuracy unless you have very accurate ball screws and nuts. I am using 1605 on all three axes and have only one on the Y also, which is my table. My frame is build mainly with 45x90 and used 30x60 for some parts. Also already now make a decision about the electrical parts, driver and controller software. Talking about electrical parts... I'd replace the Kress with a real VFD controlled spindle Even an air cooled 1.5kW would do better than that Kress, which really is only a high quality angle grinder. Even if you are not willing to throw it away, design the Z so that one day when you decide to get a real spindle you could easily install it. The Z is the most important part of a machine. If you get it right half of the battle is won, but the Z includes the spindle as well.

If you want to have a look at my specifications you can visit this post:

https://adapting-camera.blogspot.se/...nt-status.html

I don't have a real build log, but on my blog you can find many posts regarding my building progress.

Hi, my problem with the supported shaft is not the shaft itself. It's the "open" bearing that runs on it. When i put pressure on the x-axis then there is movement on the bearing...it actually distorts.
I guess a better quality bearing would fix the problem.

[ericks]

Hi, I quite agree with the moving table design as it can be made more sturdy especially if you want to get ambitious and do a bit of steel milling.

I hypothesised with a different aspect ratio design for the table size, as the table Y axis length does make the base twice as long as the table due to spindle coverage etc..

Taking a 6040 for example.....in a moving gantry design the table is narrow ....400mm wide and passes under the gantry, but with a moving table type the base would be 1.2 metres long to allow the table to traverse it's 600mm length.

You could make the table Y axis the 400mm width and make the X axis the 600mm length which means the X axis crossbeam has to be only a bit over the 600mm wide to allow the spindle to move over the table length sideways.

If the 600mm table length does not pass between the gantry uprights the head has to stick out a long way from the X axis face to cover the 400mm table width.

So, as the uprights and crossbeam can be massive, it would be practical to allow the table to move a short distance under the crossbeam but not necessarily all the way as in a moving gantry type......this would reduce the spindle stick out from the X axis face quite a bit.

At no time would you want a long job to overhang the table sides.....it can overhang on the 400mm width as that is now the Y axis.

I think a table rapid travel in a 400mm Y axis can be a lot quicker than the corresponding normal 600mm table length......it's unconventional, but could be practical to keep the base length more compact.
Ian.

That was the first thing i realized about the fixed gantry design, the length of the machine...

[A_Camera]

Hi, my problem with the supported shaft is not the shaft itself. It's the "open" bearing that runs on it. When i put pressure on the x-axis then there is movement on the bearing...it actually distorts.
I guess a better quality bearing would fix the problem.

There are two screws in each bearing to remove the play. Mine are 16mm but I can NOT feel any movement and definitely no distortion.

[A_Camera]

That was the first thing i realized about the fixed gantry design, the length of the machine...

...the calculation is wrong in that link. A moving table type requires more space than a moving gantry type, but not twice more, only about 1/3.

[handlewanker]

Hi....that only applies if the bearing blocks on each rail under the table are closer together in the Y axis length......... the spindle has to cover the table Y travel length, the closer together they are on the rails the more unstable they would be, one reason to design with the table long and across the Y axis and short in the up and down length.

Then a 400mm wide table Y move would need 800mm long in the base as opposed to 1200mm if the table was longways in the Y.....but you can reduce the spacing a smidgeon and get 700 for the wider table design........ not very practical

This also has it's drawbacks, as now the table bearing block aspect ratio is out of proportion to slideway length/travel formula.

That is, for a slide way to be a guiding factor it must be longer than wider....a wide table can overcome this to a degree by spacing the rails closer together, but also spacing the blocks on each side further apart in the long configuration.....then you have to have the double length to cover the travel.

In the end it will be realised that massive cutting forces are not in the picture, so the rail and block spacing becomes a matter of convenience.......I would say though, that if you have the space go for the double length in whatever configuration the table is.

If you wanted to very pedantic, you could use rails that are a smaller profile but use two of them on each side under the table.(my choice).......that gives you the long slide aspect ratio and apart spacing in one nut shell, also the smaller size brings the overall height down making the table more stable.

I doubt whether the different slide design factor will put any moving table CNC router light years ahead than if you followed conventional design, it's a matter of personal preference, but you can strive for perfection if that is your whim.

One very big advantage of the moving table design, and why I like it so much, is with a single central ball screw there can be no slewing of the table when the spindle is to one side as happens to the gantry on a moving gantry design, unless 2 ballscrews are used, either coupled or with 2 stepper motors.
Ian.

[ericks]

There are two screws in each bearing to remove the play. Mine are 16mm but I can NOT feel any movement and definitely no distortion.

I have removed the play with the screws. But what i have found is that if i put pressure on the tool then the bearing block's actually give way/open up...

[ericks]

Hi....that only applies if the bearing blocks on each rail under the table are closer together in the Y axis length......... the spindle has to cover the table Y travel length, the closer together they are on the rails the more unstable they would be, one reason to design with the table long and across the Y axis and short in the up and down length.

Then a 400mm wide table Y move would need 800mm long in the base as opposed to 1200mm if the table was longways in the Y.....but you can reduce the spacing a smidgeon and get 700 for the wider table design........ not very practical

This also has it's drawbacks, as now the table bearing block aspect ratio is out of proportion to slideway length/travel formula.

That is, for a slide way to be a guiding factor it must be longer than wider....a wide table can overcome this to a degree by spacing the rails closer together, but also spacing the blocks on each side further apart in the long configuration.....then you have to have the double length to cover the travel.

In the end it will be realised that massive cutting forces are not in the picture, so the rail and block spacing becomes a matter of convenience.......I would say though, that if you have the space go for the double length in whatever configuration the table is.

If you wanted to very pedantic, you could use rails that are a smaller profile but use two of them on each side under the table.(my choice).......that gives you the long slide aspect ratio and apart spacing in one nut shell, also the smaller size brings the overall height down making the table more stable.

I doubt whether the different slide design factor will put any moving table CNC router light years ahead than if you followed conventional design, it's a matter of personal preference, but you can strive for perfection if that is your whim.

One very big advantage of the moving table design, and why I like it so much, is with a single central ball screw there can be no slewing of the table when the spindle is to one side as happens to the gantry on a moving gantry design, unless 2 ballscrews are used, either coupled or with 2 stepper motors.
Ian.

Ian, thank you for the information. I will work on a drawing and post it here sometime...

[ericks]

My mate sent me a pic of the gantry beam and other bits he cut..

[ericks]

He started doing some welding today...

[ericks]

Hi everyone....i am looking at linear rails and ball screws at the moment. Has anyone bought Hiwin rails and carriages from BST Automation? If so was it genuine HIWIN??
Also the ball screws that Bst sells....are they reasonable quality?

Thanks

[paul3112]

Yes... Rolled or ground and to what standard ordered.
I have dealt with Fred at BST over the last 4 - 5 years. His factory details Chinese Manufacture for Linear Guide,Ballscrew,Linear Rail & End Support etc.??Zhejiang BST Linear Motion Co.,Ltd as opposed to the https://www.aliexpress.com/store/314742 .
Send Fred an email, he will respond. The silly question is the one you don't ask. If you have requirements for accuracy and item life tell him, ask his advice. But from experience your tool run out and frame stiffness will be more than the free play in the rails.
Rule of thumb ..add another truck ( three instead of two with extra space between the trucks so as not to align with the bolt spacing of the rails. )
Good luck mate

Paul

[ericks]

Thanks Paul

[ericks]

Update.....i have decided not to continue with the steel framed machine. My mate will continue it for himself. The machine will be too heavy for my use, plus the size was going to be too small for me. He was going to make the same for himself anyway... Well i decided to go with my original idea of an aluminium framed machine. I ordered 160 mm x 80 mm and 80 mm x 80 mm heavy duty extrusion today. Will post some images soon as i receive them. They will be cut to size and i will use my cnc machine to make the holes for the fasteners...

[ericks]

Received the frame parts today. I am very happy with the quality and service

[ericks]

Update, the machine stand is welded up....ready for cleaning and painting. Also bought the adjustable feet for the stand and machine today. Hopefully i will complete work on the stand this weekend and start machining the extrusion and foot plates next week

[zeeflyboy]

looks beautifully made!

[ericks]

Thanks, its the same footprint as my machine....I have to finish it cause i have no other surface to build my machine on

[ericks]

A little more progress......ready to start machining the extrusions and feet "brackets"

[ericks]

A little more progress today, started to machine the extrusion for the universal fasteners...

[ericks]

Messing around with the stand....decided to use a Electrical panel i had lying around, i will order a new backplate for the panel. I might keep the plc and hmi......depending on what i decide to add to the electrical controls.