The truth and nothing but the truth

[Acebull]

G'day all as the title says, the truth and nothing but the truth. I've roamed the forums on the internet for the answer and all are different. My question is, what to use, rack and pinion, lead screw or the most expencive, ballscrew. I know ballscrew is good but you need Bill Gates pockets to pay for them. So that leaves rack and pinion and lead screw. A lot of forums say rack and pinion is not good for accuracy but good for speed but wears out easier. Lead screw has problems with whipping and backlash but better for accuracy but slower. So what the hell is the truth, please help me out.

Ted.:confused:

[danilom]

Depends on the travel you need, above 1m length rack and pinion is a way to go.
In 3 years of working with MM, there was no job that needed more accuracy than 0.2 - 0.5mm which is easy on a rack and pinion drive.

[MetalHead]

Rack and Pinion with Belt Drives. Used many times here with success. Best cost to return in my book.

If this were a machine used to build Space Shuttle parts ..... but wait .... we have done that ... sorta :) !!!

Kidding aside , unless you have wicked tolerances , rack and pionion should be fine.

[Gerald D]

Also remember that cheap ballscrews have poor seals and need a lot of cleaning to keep them turning. We have found R+P to be basically self-cleaning and needing no maintenance.

[KenC]

If you can afford it, there is nothing wrong using ball screw on a CNC router; Its like wearing a 2000 dollar suit to clean the sewage pipe; Butchering with a surgical blade; Ferrari as tow truck.

[Robert M]

MMmm....a "déja vue"....here (http://www.woodworkforums.com/f170/truth-nothing-but-truth-174617/)

[Acebull]

Yes RobertM I'v posted on about 6 forums need all the help I can Get ;)

[Robert M]

6....:eek:
kidding....:p

[Acebull]

G’Day All thanks for your input what do you think of going 3/4 .500 4start lead screw for X&Y and 1/2 100 lead screw for the Z and Linear Rail for the motion the machine size that I want to build is 900mm X 1500mm I leave you to convert that as in Australia we are in metric I hope to do 2D/3D carving and scale model plane plan cut out

Ted

[KenC]

Good luck.
Have fun!

[racedirector]

Ted

I suggest you visit cnczone for general CNC building, you will find that everyone here is focused on the Mechmate design which means R&P with V-wheels on angle or V track. Not fobbing you off, just lowering your expectations of an answer on general CNC construction.

Cheers
Bruce

[Acebull]

Racedirector This ain't a Blues and Maroon thing I hope not coz as you know the Maroons are the BEST :cool::cool: Ok Racedirector Im up for any ideas to help if you can help got for it if you say R&P is the go give me some idea on like what size I would need and what size steppers and the like and if you have the time can you knock one up and drop it round to me but all jokes aside mate Im just looking for some help not got a lot so far :rolleyes:

[racedirector]

Ted

I am not trying to be harsh in any way, just saying that this forum is focused on the Mechmate design. Now, with that said, there are a couple of small Mechmate builds right here on the forum, there is nothing saying you can't build a small one. The plans tell you how to calculate what you would need to build to a specific size.

One of Gerald's earlier posts suggested building the gantry full size and shortening the table is you don't want a 4x8 (1200x2400). I toyed with the idea of building a 4x4 but I already have one of those in a different design so decided to go the full MDF sheet size.

I can speak from experience re leadscrews, I own a 4x4 machine with leadscrews - never again. Here in Aus you can't get ACME rod in fancy sizes, you will be limited to 1/2 6tpi 1 start so they must be imported from the US. The Mechmate however uses Module 1 rack, readily available in Aus from various sources and, personally, I would use R&P over leadscrew any day.

As for Maroons vs the Blues, I don't follow it :) Rugby Union here my friend and a Kiwi to boot so my support rests with the All Blacks.

Anyway, back to it. Spend a little time looking around the forum, particularly at the "junior" builds. One thing you won't regret is comprehensive plans and tons of support for them right here, far better than trying to design as you go along.

Cheers
Bruce

[KenC]

Again, not being harsh... From your questions, sounded to me like you either know nothing on transmission or you are playing idiot.

This forum is getting very "specialized" in R&P and V-Wheel configuration. So general beginner questions don't quiet fit this crowd... BUT personally, I don't rule out alternative as long as it can beat the overall performance in every aspect.

What puzzle me most is why anyone who know nothing about the subject would want to do his own design....

Since you need all the help you need, here is it...
Follow a well established plan (eg, me on MM plan), question only how to build it & find you answer why things are done in that specific way later.

PS, I would not use anything slender cylindrical thingy over 600mm that rotates over 50rpm unless my life depend on it.

[darren salyer]

IF I could build a machine that had tighter tolerances than mine currently has, I don't have the foggiest idea what I'd do with the increased resolution.
Unless I started carving The Last Supper on single grains of rice, a "better" machine would be a waste for me, and from what you say you are wanting to do, for you as well.
These machines are made to cut and carve wood and the like, a material that moves with seasonal changes way more than the three decimal points we machine it to.
Build one, then sit back and be astounded at what you can create on a machine you built yourself.

[Acebull]

Hi KenC as for your question about do I know nothing about transmission answer is not a lot that is why Im here to find out I'm a Carpenter not a Engineer and if you Google DIY CNC Routers there is a heap of them most don't use rack & pinion where Mechmate dose which is great and if you think its the way to go that is good and I can go with it as I'm easy its just I'm a bit stuck with that size because of room so why can't I change the size to what I need but sick with Mechmate design I'm sure I'm not the first to do so
Ted ;)

[KenC]

More the reason not to do your own design.

Why not waste you time on sieving through the forum instead of throwing overly general questions?

**
who said you can't change the size? only shows you didn't read...
I too changed some of the design on my builts, its because I knwo what the difference between screws & R&P... period.

[Acebull]

Hi KenC Mate if you don't wan't to help thats OK so don't bother posting on this thread but just to fill you in I'm going to build Meckmate machine but no thanks to you ;);)

[KenC]

And I thought I was helping... :)
Have fun wasting your money!

[darren salyer]

And another Newbie comes in expecting us to modify the MM design to fit their particular wants, and gets condescending and confrontational when we aren't too keen to put more effort into their build than they themselves are willing to invest.
Ace, spend at least a week of 8 hr. days reading this forum and you'll realize all the answers you are expecting to be spoonfed already exist in printed form here.

[Acebull]

:rolleyes::rolleyes::rolleyes:

[Richards]

There are a lot of CNC routers for sale at fairly reasonable prices. The MechMate is a do-it-yourself project that allows you to build exactly what you need instead of letting someone else decide for you.

If you study the designs on commercially made machines and then make a list of the parts required, you'll have an idea why some use ball-screws, why some use linear rails, why some use servo motors and why some don't.

Define your needs. See if something is already available. If not, then roll up your sleaves and start learning how to build your own CNC machine. When you're through with your build, you'll understand the assets and the limitations of your choices.

[Acebull]

Hi Richards/Mike building the machine is not the problem between myself and my son we have that part cover be it wood steel or ally it was just the drive and motion I needed help for I'm stuck with the size 900mmx1500mm as for room if you guy say rack & pinion is the way to go that is fine so I would look in to using it as I am retired and only want to build one as when you are retired cash flow is a lot less well that is in my case I hope to do 2D/3D carving and scale RC model plane plan cut out nothing to exciting I did not come here to put anyones nose out of joint it like when I us to help the apprentices they ask for help and I gave it to the best of my ability :) :)
Ted

[KenC]

Now you are talking sense :) I Like.
What you want can be achieve here.
"When money is short, time is your friend"
OK, the best way to get help is to ask meaningful question, to do that, start reading, every thread if you must, I spent at least 4 hours a day for weeks before I started ordering anything... May be its because I'm stupid... but you may be able to learn things faster.
Building is the easy part, I build 2 on my own, many other built it by themselves too. The hard part is to get to the point of build start; The hardest is after you got the machine running. All three period has its share of fun & hair pulling moment, but have no fear, we will be by your side.

[lonestaral]

Hello Ted.
I am going to start my build in an hour or so.
I will use the Rack & Pinion method.
The nut wore out on the X axis of my present machine.

I too will be building a smaller machine.
Some material sizes are different.
So I have to make some changes.
No doubt I will make mistakes, just hope they are not expensive mistakes.

Well here goes.Let the adventure begin
Good luck.

Bundaberg, I was up that way once. Famous for the rum.