New Machine Build- Which style to chose for next machine ?

[nokillzone]

Im stuck on what design to go with ..
I have 3 types i like
1) Standard design
2) Bridge style
3) Table moving while Y is stationary

Have 4 x 45inch rails and 8 blocks (--22)

have 2 x 18inch rails and 4 blocks (hsr20)

if i go with first 1&3 choices id have to use ballscrew or id like to use ballscrew's (3ballscrews 500 bux Minimum)

But with Bridge style i can use chains.. while i dont know how accurate chains are and how good they can be .. i am intriqued by it ..

Any one have any input in this ?
Thanks!

[Fish4Fun]

nokillzone,

A lot depends on what your needs are. Moving gantry reduces machine footprint and expense but you give up some rigidity. Sprockets/Chains (Belts/Gears) increase speed and cost but decrease accuracy. At the end of the day there are five primary considerations:

1) Work Envelope
2) Travel Speed
3) Accuracy
4) Rigidity
5) Cost

You can design a machine to have any four if you are willing to let the fifth go from zero to infinity. Unfortunately most DIY approaches begin with a budget, and this places limitations on size, speed, precision and rigidity. The best DIY builds involve serious thought with respect to all of the design elements and several budget revisions. The choice of frame materials, wood, Composite, Aluminum, Steel is perhaps the single largest budgetary step and can have a large impact on rigidity and precision.

A good SWAG method is to look @ "production machines" and ASS-U-ME that you will be able to build a DIY machine with similar specs for what the production machine costs. Consider any "upgrades" as additions to the budget. While I am certain many will argue they can design/build a machine bigger/better/faster/cheaper than a production machine, far more either fail completely, or only partially achieve their goal. Production machines in the size/price/speed/precision range you are interested in should also give you some insights into design considerations.

Good Luck! I wish there were a simple answer!

Fish

[ger21]

There's a lot of middle ground between ballscrews and chain. Chain is probably the worst possible option. Spend some time here, and you won't see any chain driven routers.
Acme or rack and pinion are good alternatives.

[aarongough]

Ballscrews dont have to be that expensive... 5/8" ballscrews from Roton are very reasonably priced, possibly because it's a very commonly used size:

5/8 X .200 Right Hand Recirculating Lead Screws & Nuts for Power Transmission - Roton Products, Inc.

[PaulRowntree]

Originally Posted by ger21 Chain is probably the worst possible option. Spend some time here, and you won't see any chain driven routers.

Well, to be fair Gerry, there are some DIY chain machines, and they do work when properly cared for and installed; I have cursed mine on several occasions, but once the bugs got straightened out, they go (and fast!). I don't know of any commercial chain driven machines, and that may tell an important story.

[ger21]

Sorry Paul, I missed that. I should have said you won't see many chain driven machines. I still say it's a poor choice, though. Sorry again.

[PaulRowntree]

Originally Posted by ger21 Sorry Paul, I missed that. I should have said you won't see many chain driven machines. I still say it's a poor choice, though. Sorry again.

No problem, and I agree 100% now. Chains are cheap, almost easy, but not a good choice.
Never having tried it myself, but I still think the Everman 'servobelt' is one of the most promising designs available to combine speed with precision. I have no idea about the strength.

[louieatienza]

Originally Posted by nokillzone Im stuck on what design to go with .. I have 3 types i like 1) Standard design 2) Bridge style 3) Table moving while Y is stationary Have 4 x 45inch rails and 8 blocks (--22) have 2 x 18inch rails and 4 blocks (hsr20) if i go with first 1&3 choices id have to use ballscrew or id like to use ballscrew's (3ballscrews 500 bux Minimum) But with Bridge style i can use chains.. while i dont know how accurate chains are and how good they can be .. i am intriqued by it .. Any one have any input in this ? Thanks!

I think you should ask yourself first, what exactly do I want to machine with my CNC? Then what level of accuracy do you need to machine to? And also how hard or easy is it to machine your material?

I think personally it would be a travesty to use precision linear rail with chain! Or at the very least you're throwing the accuracy of the linear rail and block away, using a relatively inaccurate positioning system like chain. I think even precision ACME screw and anti-backlash nuts are inexpensive enough; though with any system there'll be trade-offs.

Mike Everman's ServoBelt system seems fast and accurate, but you'll need some decent machinery to build the drive system. You could also direct-drive your axes with belts, and there are a few builds (check the Momus forum) that do it that way.

[smreish]

Visit Mechmate.com
The gantry style machine is a very robust, easy build. I personally have built 3 and they perform well as an industrial asset to my company.
It utilizes a rack and pinion style transmission system, but reliable after 3 years of hard use.

Good luck in your fact finding and decisions.

Sean

[nokillzone]

What you guys think ???

Steel + Aluminum design ......

[PaulRowntree]

Originally Posted by nokillzone What you guys think ??? Steel + Aluminum design ......

Can you move the X axis blocks farther apart on the gantry sides? It would increase the stability. Plus, the router looks like it is barely within the footprint of the X bearings (ie it hangs out beyond the gantry supports) which causes larger leverage and reduced stability. Tilting the gantry sides back away from the tool position can help with this.

[Cosworth]

Originally Posted by aarongough Ballscrews dont have to be that expensive... 5/8" ballscrews from Roton are very reasonably priced, possibly because it's a very commonly used size: 5/8 X .200 Right Hand Recirculating Lead Screws & Nuts for Power Transmission - Roton Products, Inc.

Man, I wish I knew that before I designed mine around acme screws. Every ballscrew I'd seen was so stupidly expensive I gave up on them. I'll have to keep this link in mind when I get around to making another machine.