Precision fast DIY CNC

[Litemover]

Hello everyone,

This is my first post here, and wow, what a mother load of info on this site, thank you all for making this the most informative place on this.

I'm fairly new at all this, but am raring to go with a good budget to build a premium CNC build. What I'm wondering is this. Which of these open source machine builds would be the best combination of speed and precision for high quality detailed woodwork at 48"x96" or larger? I've been looking at the Kronos KRM02, and it's pretty sturdy looking, but has Nema 24 motors. Looking to build something with Nema 34 motors and high quality drivers. Is there an easy way to convert the kronos to Nema 34? Does it really matter if it is Nema 34?

To give you a background, I will be making large scenic pieces, steps, risers, etc. Some very detailed pieces, and some not so detailed pieces. Usually time is of the essence, so speed is a necessity.

Many thanks in advance for any advice anyone can give me.
Chris

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[ger21]

Which of these open source machine builds would be the best combination of speed and precision

You only listed one.

If you're talking about the 8020 machines, most of them use components from CNCRouterParts.com

First, even with the Nema 23 motors, the spindle will be the limiting factor in how fast you can cut unless you spend a few thousand $$ for a 5HP spindle.
And I think at that point, you'll find that the aluminum extrusion and skate bearing carriages are not really up to the 5HP spindle.

I haven't seen anyone mention that precision is an issue with any of these machines. Stepper powered machines will always have to trade speed for precision, due to the fact that a steppers torque falls off with rpm, and the only way to get more precision is to spin the motor more times, which equals faster.

Imo, if you need more speed than you can get with the Nema 34 rack and pinion drives from cncrouterparts, you'll need to go with servo drives, and ideally custom made drive components with a much higher reduction ratio than the 3:1 that everyone is using with steppers.

[jalessi]

Chris,

I believe one of the CNC Zone members (msimpson99) is the originator of the Kronos KRM02. I also believe he uses some of the cncrouterparts.com parts in the construction of the machine you are referencing.
You should be able to fit there nema34 mounts in place of the nema23 mounts.
See link below:
CNCRouterParts

Sending msimpson99 a P.M. should expedite any questions you have.
He was on the Zone earlier today.

Welcome to the Zone,

Jeff...

P.S. Gerry's information is spot on, I was typing my reply when Gerry posted.

[Litemover]

You only listed one.

If you're talking about the 8020 machines, most of them use components from CNCRouterParts.com

First, even with the Nema 23 motors, the spindle will be the limiting factor in how fast you can cut unless you spend a few thousand $$ for a 5HP spindle.
And I think at that point, you'll find that the aluminum extrusion and skate bearing carriages are not really up to the 5HP spindle.

I haven't seen anyone mention that precision is an issue with any of these machines. Stepper powered machines will always have to trade speed for precision, due to the fact that a steppers torque falls off with rpm, and the only way to get more precision is to spin the motor more times, which equals faster.

Imo, if you need more speed than you can get with the Nema 34 rack and pinion drives from cncrouterparts, you'll need to go with servo drives, and ideally custom made drive components with a much higher reduction ratio than the 3:1 that everyone is using with steppers.

Thank you for the info,

Ahh, does all of that fall outside the realm of the DIY machines? Using servos and so forth to get more torque for a 5hp spindle? Also, is the 5hp spindle able to be used in EU voltages? I think I'd be happy with something equivalent to the Shopbot Alpha but if there is an easy way to get more power, then I'd do it.


Cheers,
Christian

[Litemover]

Chris,

I believe one of the CNC Zone members (msimpson99) is the originator of the Kronos KRM02. I also believe he uses some of the cncrouterparts.com parts in the construction of the machine you are referencing.
You should be able to fit there nema34 mounts in place of the nema23 mounts.
See link below:
CNCRouterParts

Sending msimpson99 a P.M. should expedite any questions you have.
He was on the Zone earlier today.

Welcome to the Zone,

Jeff...

P.S. Gerry's information is spot on, I was typing my reply when Gerry posted.

Very cool, thank you for that. I'll send him the message and see what is possible.

Chris

[ger21]

Ahh, does all of that fall outside the realm of the DIY machines?

That would depend on your skill level and budget. There are a couple DIY machines that cost upwards of $25,000 here.
There are also plenty of machines using servos, but steppers are far more common. Expect a servo setup to run between 2-5 times the cost of a stepper system (G540 based).

A 5HP spindle should be able to be run on 240V power. You just need to get the correct FVD FOR Your application.
A Chinese 5HP spindle from Ebay is about $800 + the VFD. If you want one not made in China, it'll probably be closer to $3000 + VFD

[Litemover]

That would depend on your skill level and budget. There are a couple DIY machines that cost upwards of $25,000 here.
There are also plenty of machines using servos, but steppers are far more common. Expect a servo setup to run between 2-5 times the cost of a stepper system (G540 based).

A 5HP spindle should be able to be run on 240V power. You just need to get the correct FVD FOR Your application.
A Chinese 5HP spindle from Ebay is about $800 + the VFD. If you want one not made in China, it'll probably be closer to $3000 + VFD

Thank you for the reply. I'm interested in a well proven design with servos, or some other closed loop system. As far as skill, I can draft 3d well enough, but am not a mechanical engineer by any means. architectural/Electrical drawing/following plans is something I can be decent at. Any recommendations for a closed loop system that can cut wood fast and do relief sculptural with MDF fast?

Obviously, I've come here to avoid paying the 15k-25k shopbot price, so what can I make that would cut wood as fast as those while paying a fraction of that cost? Any build hints? Do the 8020 and so forth cut wood in relief? Also, I've noticed that there are a considerable amount of 4 axis setups, but how do you get the 4th axis, as they aren't in the plans?

Super grateful for the help here guys.
Thanks,
Chris

[OCNC]

Have you looked at the Mechmate. There's a video on youtube of it surfacing a table a 1150ipm.

[Litemover]

Have you looked at the Mechmate. There's a video on youtube of it surfacing a table a 1150ipm.

That looks good, the mechmate, thanks for the link. How much does it cost to get into one of these? Any ideas? Looks perfect for what I need.

Chris

[OCNC]

How much does it cost to get into one of these? Any ideas? Looks perfect for what I need.

Chris

I read through one thread on the mechmate forum regarding a machine that someone bought on ebay and it looks like the original builder spent $6800 on it. It was a 5' x 10' machine and it's build from two years ago is documented on the mechmate forum as machine #5.

[ger21]

There's a member here who's built a few and says you can do it for $3000, but I think you're looking at closer to $5000-$7000. Could be more, could be less. Far too many variables to give an accurate price.

As for the 4th axis, most are homebuilt, and I haven't really seen any plans for them.

Any recommendations for a closed loop system that can cut wood fast and do relief sculptural with MDF fast?

Define fast? Hardly anyone here uses closed loop systems, as they're really not needed unless you want very high performance, which can cost more than most complete machines.

[Litemover]

There's a member here who's built a few and says you can do it for $3000, but I think you're looking at closer to $5000-$7000. Could be more, could be less. Far too many variables to give an accurate price.

As for the 4th axis, most are homebuilt, and I haven't really seen any plans for them.


Define fast? Hardly anyone here uses closed loop systems, as they're really not needed unless you want very high performance, which can cost more than most complete machines.

Oh cool. I thought in order to cut 10" per second, I would need something higher performance, hybrid drive, or something that can utilize a 5k w spindle. I'm working with some fairly intense deadlines is all. Most of the time, we are under the gun, so speed can mean the difference of making or not making the trucking deadline.

But, I would definitely be willing to get a slower end machine for projects without intense deadlines on them. Any ideas about what type of spindle I ought to go with?

I can foresee a considerable amount of MFD carving in relief.

Many thanks,
Chris
Chris

[ger21]

If you need to cut at 600ipm, then I'd say you need a machine with AC servos and a minimum 5HP spindle. I'd expect to spend $7000-$10,000 or more.

I'd recommend an HSD or Colombo spindle, but they're not cheap.

[Litemover]

Thank you for that, the columbia looks awesome. Are the Hybrid drives any good as I've been looking at the hybrid stepper closed loop systems and think that might be the way to go? The PRS alpha by shopbot gets 600ipm and it uses Vexta hybrid closed loop steppers with HSD 4HP High Frequency Spindle. This was originally the system I wanted to get but I couldn't afford the 21k price tag. 6-7k would be ok I think if I could find a good, reliable DIY plan for it.

Thanks for all the advice guys, very grateful for it.
Chris

[ger21]

I think the Vexta steppers on the Shopbot run about $1000 per motor and drive.

[RomanLini]

How does that old saying go?

"You can build your CNC machine; big, fast, cheap. Now pick two!"


Once you are talking 5hp spindle they are very heavy and then chassis costs go right up as you need a chassis capable of moving all that weight around at high speeds without flex and drive costs go right up to match.

In a production environment you might be better off with two medium speed machines instead of one high speed machine?

[rowbare]

You mention that you are going to do a lot of 3D contouring. In that case, you might want to sacrifice a bit of speed but build something with better acceleration characteristics. You will get better overall performance since you spend so much time changing directions when contouring.

bob

[mactec54]

Litemover

As for Ac servos, Dmm have the best choice for what you want to do, you will need a smooth stepper or similar to get the max speed,from the motors

DMM Technology Corp.

[Litemover]

You mention that you are going to do a lot of 3D contouring. In that case, you might want to sacrifice a bit of speed but build something with better acceleration characteristics. You will get better overall performance since you spend so much time changing directions when contouring.

bob

Thats helpful , thank you. How would i go about doing that is the question? Does this favour servos?

Cheers,
Chris

[Litemover]

Litemover

As for Ac servos, Dmm have the best choice for what you want to do, you will need a smooth stepper or similar to get the max speed,from the motors

DMM Technology Corp.

Awesome, thanks, do these monitor all axis simultaneously?