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joedesu1
05-13-2011, 01:25 PM
Hi,
I am planning on a usable 4X4 cnc plasma build real soon. I read through all the forums here and was given a wealth of knowledge from the pros who have been here before me. What I am looking to do is build a machine very cheaply. I am a precision grinder so I am planning on cutting corners by building everything I can (possible linear rails,tracking systems things like that) myself. I plan on using I stressed relieved I-beam as the gantry supports with high precision lead screws tucked underneath the I-beams on both sides for my X-axis. I will precision grind all I-beams to flat and parallel to .001 and will build and heat treat my own ways for the gantry to ride on, which will be blanchard ground once installed and checked for parallelism and flatness. I have read a lot about the different drive system such as rack and pinion, lead screw, and belt ect. I would like feedback on my idea to use lead screws vs a rack and pinion beside the obvious cost. I am also totally lost when it comes to selecting the proper gearing for both lead screws and rack and pinion. I know I should strive for 5/1 @800rpm but I don't really understand this concept. For the y-axis (gantry) I plan on using a linear rail I build and a lead screw as well. Any advice will be greatly appreciated. CAD files to follow soon. Thanks in advance

joedesu1
05-13-2011, 01:47 PM
Ok so I read a thread about lead screw being to slow for the cnc plasma process. Guess its a rack an pinion ill go with. Any suggestions on pitch and size for this particular set up? Thanks

aussiecncer
05-15-2011, 03:54 AM
First post here :D

I've been looking at this forum for a very long time and are currently designing my build table as well. Same size 4' x 4'.

I have also come to this point and am just as curious to find out what others suggest. I finally found a distributor for all the parts I need. I'm using Type 2 V rail all round.

When it came to the Rack size I was looking at a Module 1 size rack with a 15 tooth pinion.

I too would like someone to share their knowledge on what is the best to go with.

mactec54
05-15-2011, 09:56 AM
joedesu1

Do you have a link to the V-rollers you were planing on using, I don't think they are a good choice for a machine that size

In your case a rack is a good choice for what you want to do, But not better than a screw

Kentuckyfarmer
05-15-2011, 12:25 PM
A few thoughts, plasma can and will run at speeds over 300 inch per minute, lead screw will develop sever whip at that speed, gear rack will not.
Moore gear is one of the best source for rack, mine is 1/2 x 1/2 inch 20 deg 20 pitch, mcmaster car has the spur gears. It sounds as accuracy is your major concern and cost gear rack is a hell of a lot cheaper than precision groung lead screw will be.
No 2 sealed vee bearings can be had from amazon for about 12.00 $ each they will support way more wieght than needed for a plasma table.
I am not trying to critisize your choices, just offering some hints to a few things i have learned the hard way. With that said build it to suit your self because that is why we build our own in the first place.
One last thought if you use height control on your torch perfectly flat ways are not a must because the thc will comp for unlevel surface.
Hope some of this helps, let me know what type motor you are using and the final drive ratio can be figured out.
Mike

joedesu1
05-15-2011, 01:54 PM
joedesu1

Do you have a link to the V-rollers you were planing on using, I don't think they are a good choice for a machine that size

In your case a rack is a good choice for what you want to do, But not better than a screw

First I would like to thank you all for the replies. I am still uncertain about the v rail. I am for sure going with a rack and pinion and I agree with the advice on lead screw whip as well as speed issues. As far as the railing goes I am still thinking about my own design. I attached a pdf of a very basic design. This will run along both y-axis's and will be around 4' in length bolted to the precision ground I-beams and maybe 8-12" on the gantry arms, which will ride on way oil. Let me know what you think. I am planning on roughing the material out and then hardening it to rc 60 and finish grinding it on my cnc surface grinder.

Kentuckyfarmer
05-16-2011, 06:46 AM
The one problem i see, is the dust and grit issue, plasma leaves a major mess,
but you can build shields, wippers etc.

joedesu1
05-16-2011, 10:54 AM
The one problem i see, is the dust and grit issue, plasma leaves a major mess,
but you can build shields, wippers etc.

I thought about that last night. Looked into bellows and the things are expensive as hell. I do like v rails but I would rather use the $200+ elsewhere, like a plasma cutter upgrade. Ill think of a solution soon, I am ordering my material today so I better get it all finalized.

Kentuckyfarmer
05-16-2011, 12:45 PM
Joe just a thought, if you have the ability to custom grind shapes etc, take some 1/4 cr and grind and make your own vee rails, the theory behind the vee wheel is it self cleans as it rolls.
BTW where are you located?
Mike

joedesu1
05-16-2011, 12:54 PM
Joe just a thought, if you have the ability to custom grind shapes etc, take some 1/4 cr and grind and make your own vee rails, the theory behind the vee wheel is it self cleans as it rolls.
BTW where are you located?
Mike

Mike,
Hi I was thinking about that this morning. I run a cnc profile grinder at work among other machines. I can dress radii, angles, ect into and wheel and grind the profile into a part. I can even creepfeed up to .060 off in one pass. I am located in Alameda CA and my shop is in Oakland CA

mactec54
05-16-2011, 02:25 PM
Kentuckyfarmer

It take's a whole lot more than just some 1/4 Crs steel to make the V-rails, & as for the cleaning action of the wheel I hope you are just joking, This does not happen

For a plasma machine anything but V-rollers would be better, You are building a large machine you need good support were it's needed, the Z could be V-rails but not the rest of your machine

joedesu1
05-16-2011, 02:34 PM
Kentuckyfarmer

It take's a whole lot more than just some 1/4 Crs steel to make the V-rails, & as for the cleaning action of the wheel I hope you are just joking, This does not happen

For a plasma machine anything but V-rollers would be better, You are building a large machine you need good support were it's needed, the Z could be V-rails but not the rest of your machine

Mactec54
So looking at the pdf for the rails I planned what do you think? I think anything that is precision and ground to tight tolerances will have a cleaning action to them. I am really up in the air with this one.

mactec54
05-16-2011, 03:36 PM
joedesu1

Any grit dust from the plasma cutting, would, not good for what you were planning
The x & y axes needs to be guided very well

In your design you need to get the X axes sheilded as best you can, like up side down under, away from the table top, this will help to keep the plasma cutting grit & dust away from the sliding surfaces, So the cheapest would be supported round rails or a skate bearing set up

Kentuckyfarmer
05-16-2011, 09:27 PM
mactech just what type of plasma table are you running? Most of the home built tables have gantrys that wiegh under 200 lbs that does not seem to be a problem for 4 vee bearings to handle.
The most important thing is for all parts to be rigid little or no flex or play. As to precision or flatness a good thc system will compensate for a slight uneven rails.
If you are building a machine that will ru 24 / 7 it needs way more than a home shop table would as for wear points etc, BTW it would be a boring world if everyone did things all the same way, there is more than one way to skin a cat

Dustin407
05-17-2011, 02:37 AM
Kentuckyfarmer

It take's a whole lot more than just some 1/4 Crs steel to make the V-rails, & as for the cleaning action of the wheel I hope you are just joking, This does not happen

For a plasma machine anything but V-rollers would be better, You are building a large machine you need good support were it's needed, the Z could be V-rails but not the rest of your machine

Mactec,

I think your advice blows.... :eek: I am running v wheels/rails on my y and x axis and never had one issue, so what if dust gets on the rails. Why does that matter. You need to worry about large particles and they just slide off.... Can you balance a ball on the point of a triangle?? If your so worried about the dust just place a small neodymium magnet in front and behind the v wheel, it would pick up everything instantly... (outside the box)

Joe,

Use the v-wheels/rails. Super accurate, cheap, durable, all around awesome for plasma... I would also make your own v-rails if you could. Basically its a 90 deg. angle rotated 45 deg, so the points verticle, pretty simple to machine on a mill. Its better to save your money for other things than expensive rails that are not going to benifit you in anyway. Good Luck on your build BTW....

mactec54
05-17-2011, 08:16 AM
Dustin407

How big is the machine you have them on, & how often do you use it??

There has been a lot of builder use the V-rollers, only to have to change them after a very sort time of use,(The information is here on the Zone)it's not the dust thing that is the problem, the standard v-rollers in this application just don't last, If you have a very light machine they will work, But most builds are not light so they will not last for any length of time

I have used hundreds of V-Rollers so I know what & were they are best used

mactec54
05-17-2011, 10:14 AM
Dustin407
Quote
I think your advice blows....Use the v-wheels/rails. Super accurate

How can anyone give advice on what is best for the machine he wants to build when there is no plan/drawings of what he intends to build

If you look at this plasma machine that Heavycnc is building & say, you should use v-rollers, We would be able to hear the laughter

As I have said before V-rollers have there place for light duty work

You say super accurate, They are not & never will be

2 photos of heavey & light build, is by ezrouter using the v-rollers running on the edge of angle iron, which is good enough for a light machine

joedesu1
05-17-2011, 10:37 AM
Mactec,

I think your advice blows.... :eek: I am running v wheels/rails on my y and x axis and never had one issue, so what if dust gets on the rails. Why does that matter. You need to worry about large particles and they just slide off.... Can you balance a ball on the point of a triangle?? If your so worried about the dust just place a small neodymium magnet in front and behind the v wheel, it would pick up everything instantly... (outside the box)

Joe,

Use the v-wheels/rails. Super accurate, cheap, durable, all around awesome for plasma... I would also make your own v-rails if you could. Basically its a 90 deg. angle rotated 45 deg, so the points verticle, pretty simple to machine on a mill. Its better to save your money for other things than expensive rails that are not going to benifit you in anyway. Good Luck on your build BTW....

Dustin407
Thanks for the advice. I am still debating what Ill use. I definitely will not be using expensive rails though. My whole thing is to build everything I can myself to save $ and to say that I built 90% of the machine.