VMC Mill Discussion

[Tkamsker]

Hi people
there is a thread called "Show how to build a CNC machine from the very beginning to the end" where a chinese manufacturer attracted people how to build an CNC Machine (similar to Tormach, Novakon, Syll, Optimum machines ) some people (like me ) have invested and since long time nothing has happened ,..
So while waiting there is in that thread a discussion about VMC mill designs.

Do this thread will be in general about pro cons and designs stuff of this kind of machines. And i will make my requirements clear.
Hast to be able to do Steel , X axis 400mm y axis 200mm Z axis 200mm or bigger.
CNC is a must. It should not stall and small batches should be able as well. Later an ATC would be nice.

So sayed that there is the possibility to retrofit an "old" VMC mill (you can search for my Bridgeport 412 Retrofit thread so i know what i am talking about ) this option is not covered here.
And i will also do no look on mach3 , linuxcnc or similar i expect servos or steppers in that size of machine.

Machine Frame :
there was an discussion if it has to be casted or can be welded in steel.
I think it depends of the quality of steel if you have good quality steel why not weld it there is an given wall thickness you need for the needed strengt.
So in my opinion there is no need of cast for an VMC mill

Linear Rails or dovetails.
i have seen heavy and precise dovetail an machines (deckel or similar) i personally think that proper dimension linear rails make more sense for an cnc machine because the friction is less. so fast and small moves will work better.

Ballbearing Spindle.
I personally think that this is the hart of an cnc machine and has to be also properly sized and high quality.

Drives.
Depending on the requirements i think that in small sector overpowered steppers are acceptable. and in closed loop there is only the end speed the differiaenciator of servo and stepper.
If my intention is alu and high speed feeds then an servos system might be a good choice so i think that in that case the manufacturer should offer that option.

Spindle.
Here i guess it is complicated and depends on that requirement
for instance on my CNC Router i insist on ATC why because i do PCB´s with it. When i have to mill ALU i change the spindle and use the normal Kress with it.
But sayed that i think that the ISO30 Spindle is more expensive but has more pros that cons (i never worked with an R8 of tormach )
I guess that often used tools can be prepared and known by tool database
i also have the advance that the spindle motor force is mechanically transportet by this small blocks.
If the BDLC motors are really that big advantage i would like to hear your opinions

Fazit
If i look for instance on an optimum BF46 and the cnc optimum i can not see why this should be an bad optimum ?
Mr Handlewanker gave me the impression that there is something bad by using the frame of an stable VMC mill and use it as CNC
i have now looked all the dfengs pictures through and can not really see the big advantage.
it seems that cast is cheap compared to EU (i guess less regulations cheap energy ) but i would like to see where is really that big thing.
i almost bought an Syll machine and they are also straight forward.

so i am looking forward for an nice and constructive discuss

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[G59]

Subscribed to this thread. I think it should be focused on quality and accuracy. I couldn't see what the big hoopla was about the defeng machine, other than 'cast'. Nothing new or special for me.
A well designed, welded steel plate machine is possible especially if you strategically place vibration dampening materials in the right areas..
Finally more into the DIY realm.

[LeeWay]

A few thoughts here.
If starting with a welded base, I don't think the type of steel for the tube is actually all that critical. I think the actual mounting pads or plates would be where you might want a higher quality steel.
Weld those parts onto the tube. Include thick gussets in the design where possible. That or incorporate then into the design. Like at the base of the column. Perhaps the head to Z plate mount, depending on the design.
I assume some sort of stress relief will need doing before the pads are machined? I also assume that you may want to fill the tubes with epoxy granite or something. I would leave a provision in the design to do this after receipt of the mill. Most of the aggregates can be sourced locally by all, so would not need to pay shipping charges on rocks.
Just a few thoughts. Look forward to this treads discussions and your progress.

[aarggh]

I agree with Lee, nothing beats sheer mass for a mill, so designing it so mass can be added after receipt by the customer would be a really good way of reducing costs and build time required.

cheers, Ian

[G59]

I also agree with Leeway, very ingenious and would save on shipping and possibly facilitate assembly. Pure mass is however not always the best. Good for the foundation, but inherently problematic when trying to achieve rapid moves along with accuracy. What we need is a balance of all the variables combined so we can ensure a top of the line machine that is durable, predictable and reliable, all the while being serviceable.
A good example is the Brother machines TC32. Incredible speeds but at what costs? Large motors and controlled by proprietary motion controllers that would throw this build into the stratosphere. A RoboDrill is another example of over the top.
We also must remember that with the new HSM toolpaths available, pure horsepower or massive assemblies are not always required. Sometimes a faster spindle and quicker motions that can compensate for the lack of torque, can achieve the same results if not quicker, than the old hogging mills. . Look at a Datron M8 for example. Looks like a router on steroids but is truly a machine with great finesse.

[asuratman]

Hi,
This will be interesting discussion. I will subscribe to this thread. Does this thread will discuss on designing a good cnc mill from ground up? Not retrofit?

[LeeWay]

Another thing to mention. I just finished up tramming my Pulsar last week. Of course, it required shims. I keep plenty of it on hand. However, with some forethought in design as is being done here, the column could have shim pads on each corner. Might not work as well on a large machine, but it would make short work of tramming on a machine this size. I don't think you would loose any strength with them.

The head also needs attention with regard to tramming. I know that good accurate machining of the assemblies will negate most of the need for tramming, but there is always that bit that may need adjusted. They make set screws with swivel pads on the bottom. Those might be perfect for such an application.

I also think the Y motor must be at the rear. The motor in the front would take up some very valuable real estate.

One other thing that I really like about the Pulsar is the SS way covers on Y. Having them on Y and Z make a lot of sense to me. They have to be easily removable though. That goes along with easy service.

[G59]

That's what I'm hoping for. Something new.

[G59]

Hast to be able to do Steel , X axis 400mm y axis 200mm Z axis 200mm or bigger.
CNC is a must. It should not stall and small batches should be able as well. Later an ATC would be nice.

Seems reasonable? Is this build going to be all metric?
Can we agree on 10,000 rpm ISO or BT30 spindle? 2.2kw power(3HP).
Single Phase 230-240Volts?
AC or DC servo drives.
Our own software or another Mach3 make it work project?

Many questions, but interesting to say the least.

[asuratman]

Tkamsker,
Will you start with CAD drawing?

[LeeWay]

I hope we might plan to use Mach 4. Surely it's getting closer now.

I would say we would need a Cad drawing once some sizing is figured out. I'll start by saying that 3/8" thick tube is probably plenty for the skeleton. Thoughts?

We would need a width and height dimensions and lengths can be determined later. I haven't actually drawn anything in SolidWorks yet, but it manipulates that kind of change easy in a drawing.
I have to erase the screen in TurboCad.

[G59]

My problem with Mach4, is it's relatively new and exactly how will it communicate with the controller or drives. I'm unfamiliar with it. Does it still use a BOB of some sort? Ethernet maybe?
As for ground up software, I think that's just too big of a bite.

Definitely need some CAD drawings.

3/8" tube has enough meat to be welded on and very rigid for that size machine.

[LeeWay]

Mach 4 isn't released yet. It should be left as an option I think. That is unless he sets on something like Flash Cut. Maybe Kflop, though I know nothing about either of those. I don't know anything about Mach 4 for that matter.

Drives and motors can be sorted out easily enough I think. Digital drives would be nice. AC steppers would work okay in this size machine, but could spring for Servo's. I would go AC over DC.
Defeng got caught up in making enclosures as well. I would think that to keep shipping costs reasonable, enclosures and stands should be sourced locally.
Perhaps provide some plans so a local guy could fab them up.
What you would save in shipping will easily make up for that cost. You can have it made like you want it then. Keep that hassle off the supplier. He will have his plate full with just the machines.

[frigger]

The control software shouldn't even discussed, it should be left to the end user to decide what electronics and control he wants to use to run his machine. Too many options available, I might prefer Linuxcnc and servos to your steppers and Mach 4, kflop, edging cnc, etc, etc. Just build a good base machine and let people accessories on their own with maybe belt drive or direct drive mount option for servos or steppers.

[LeeWay]

The control software shouldn't even discussed, it should be left to the end user to decide what electronics and control he wants to use to run his machine. Too many options available, I might prefer Linuxcnc and servos to your steppers and Mach 4, kflop, edging cnc, etc, etc. Just build a good base machine and let people accessories on their own with maybe belt drive or direct drive mount option for servos or steppers.

Actually, that is not a bad idea either. Bare bones so to speak.
A CNC ready mill. I like it.

[inov8r]

I think you guys are pretty much describing this build from 2007! I am diggin the solid base

http://www.cnczone.com/forums/bencht...htop-mill.html

[Tkamsker]

Hi i will Not discuss Control Software (i personally am in it for > 30 years so on my machine no Windows for sure ) because it doesnt matter if you use fanuc Siemens linuxcnc or whatever you like i might for that do an extra thread )
Inovator this picture is an Good example what i want to compare it Looks like an rigid Walder Frame
I ll Digg in my picture Fundus and lets See what we all think
,..


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[Tkamsker]

Hi,
I agree with Leeway and G59 there is to be a balance of table weight and your intended pieces like
Here you see the table of an Bridgeport 412I which allows Pieces to be milled of 350kg ! in the back you see the SEM Servo which can do 8-17 NM and draws 75A !!
but even that servo is belt driven , or another example This is an BF 46 CNC kit but dovetails . And here dfengs solution
I personally think that the basement is cast it makes it verry heavy but i don't see the advance in that configuration (Size and force ) i also have the feeling that the base where x and y axis are connected it is too high.
So if you really have a heavy piece of iron to mill it will stress the rails. where probably dovetails would have a benefit.
Now we come to size and connection of servos/steppers.
Here defends solution and to compare the solution on my machine

I now think if you have the need of speed (alu copper and long traveling of x and y axis ) it may be senseful to have an oversized servo on direct drive ,.. (there i would be interested on your opinion because of pid there may be markings on the goods ) but if i do steel and a lot of 3d work which is mainly little steps and slow speed (what my config is intended to do ) the stepper with an belt drive is an ok sultion i will have force enough but less high speed.
I am now calculating the costs of closed Stepper (nanotec ) and german control (triple beast ) and yes it should work with mach 3 - against an taiwan servo combination using granite devices VSD in dual mode
to see how big the price difference is.

[LeeWay]

I agree that the XY saddle could be shorter.
I think too that it should have a moving table on stationary rails. Like Chris and Arie built. When I first put my 80/20 mill together, it used a traveling rail with stationary trucks. I quickly switched it over to the traveling trucks. Much better layout. It does require a way cover on X in this case, but the benefit is that there isn't any table droop at the extents. On mine, I happened to have two extra trucks. I installed them in between just because I had them. That is 3 THK HSR25 trucks on each rail of a 14" axis. Overkill. Yeah. But it is pretty solid. There is virtually no machining ever done that isn't right over a truck.



Another reason for this type table is that they are smaller. Since this would be a welded frame machine, no need to cast a table. The table could be machined from Cast iron or steel stock.

The idea of a smaller steeper with belt drive might be fine on the Z axis, but I think larger direct drive motors have fewer moving parts and therefore easier to maintain or service. By the time you figure the parts and labor on the belt drive, you have already passed the cost of larger motors and drives.

Cover plates or way covers are not too labor intensive if they are designed right along with the rest of the machine.

[G59]

By the time you figure the parts and labor on the belt drive, you have already passed the cost of larger motors and drives.

I agree.

Personally, I would go servo. In my opinion analog drives are best, but with digital having such small incremental steps and pulse smoothing, it may actually be the same. The reason I mentioned Mach3, was because it's open loop nature is a big disadvantage in my books. So, no talk of control software is fine by me.
Cast anything is money. Unless you are going that way and will be selling the parts.

Have you decided on the work envelope? That will pretty much give you the table size needed.