Now I see relatively small ratios used (3:1-5:1) being used on lead screw type tables where chain driven table are more like 30:1+. Is this because
a lead screw arrangement gives you increased torque multiplication and resolution by it's own inherent design vs. the chain drive?

Is there a place that sells these cheaper?

A lead screw with 5 threads per inch would move the tool 1/5" for 1 revolution of the shaft. (5 revs=1")
A chain with a sprocket of 3" Dia. moves the tool 9.4" per rev. (5 revs=47")

This comparison tends to show why different ratios of reduction are used for the two drive methods.

My reducers are worm gear type, purchased from Princess Auto in Canada, & their catalouge (http://www.princessauto.com/PAcountry.cfm?CTRY=CAN&INF=home)still shows the 60:1 unit I used @ $100. (About page 70??)
There are likely other sources for this imported item which has given excellent operation on my machine.

I hope the truck drops something on your lawn!:)
You can build it.
WT

Leadscrews have severe limitations for plasma construction

1. The plasma process is dirty and deposits abrasive and conductive soot on all exposed surfaces. Leadscrews need lubrication. Lubrication holds the soot.

2. Leadscrews have upper RPM limits because of lead whip.....the faster you spin a leadscrew the more it "bows" from centrifical forces. Depending on the pitch you will find they top out at speeds slower than you need for plasma. The "whip" is a factor of the screw diameter, the length (from bearing to bearing, and the type of bearing mounts.

Belt coupling at the motor is better in a lot of ways than direct coupling. Vibrations of the mechanics are not transmitted to the motor and vice versa. The resonance model is a lot simpler.
The ratios can be adjusted simply by changing pulleys and belts. Broken belts are rare but if they occur spares are cheap and easy to change. It allows the motor to be offset which can result in a lower profile and protection for the motor. On a table that moves rapidly and large distances not having motors hanging out of the sides can save you from some accidents and down time.

A leadscrew changes the speed/torque-resolution ratio by the number of TPI. So instead of a step up you get a step down. That would indicate that you need no further reduction for steppers and smaller amounts for servos. Once again though, your limiting factor becomes the max RPM of the screw itself. Most will not tolerate more than about 600 to 1000 RPM. Divide that buy the TPI and you get the IPM that will give you....a standard 5 TPI leadscrew (or 10 TPI 2 start) limits you to no more than 200 IPM (probably less) and at least a 5/8" screw size. That works just fine for most routing applications but is below what you will need for plasma with thin material.

TOM CAUDLE
www.CandCNC.com

Everyone needs to have a firm understanding of the drive train basics and know how the ratios effect the load movement. Ultimately you will have to enter the number of steps it takes to move the tool one unit of measurement (inches or mm).

The choice to go rack and pinion and use more cost effective toothed belt reduction between the motor and pinion is a trade out to get sufficient rapids, lower cost and the flexibility to have a dual drive gantry for wider tables.

Thanks a bunch for for all the info.

Tony

Weldtutor

I have looked at your great examples done with your setup. Have you done any thicker material cuts? (1/4"-3/8")? Part of my planning involves the actual plasma cutter. I am leanning towards the Cutmaster 52. Most of my cutting will probably be around 1/4".

Thanks
Tony

Have you done any thicker material cuts? (1/4"-3/8")? Part of my planning involves the actual plasma cutter. I am leanning towards the Cutmaster 52.

This photo shows the excellent cut quality of the edge of a 1/4" steel section of an agricultural machine component.

It was cut with the Thermal Dynamics Cutmaster 51, on my CNC machine, both of which are shown in the earlier postings.

I've cut 3/8" mild steel manually with the Cutmaster 51, & obtained very good results, but have not had an application requiring the CNC unit.

Loons are now nesting near our northern lakes.:drowning:

The one pictured below was cut from 14 ga. steel & coated with hammertone black paint.
Life size overall length is 22".

Weldtutor, I have been following your build for a while and am getting ready to start my own build. My plan is to build a table that will handle a 4x4 piece of metal. I recently purchased a used Hypertherm Max100 Plasma cutter. I am planning on starting to build my frame and drive mechanisms while saving money to purchase the PlazPak from candcnc.com. I have a couple questions I hope you would answer for me.

I found the gear reducers that you used but I am in the US so I need to find a different supplier. I found a few different reducers on surpluscenter.com's website but I am unsure whether they would be ok to use from a backlash standpoint. With the accuracy of plasma will backlash be something I need to worry about or would most worm gear drive reducers work?

For your chain drive parts, what size chain and gears did you use to work with the 60:1 reducers? I found surpluscenter.com also has many chain drive parts but I wasn't sure which size(s) would be best for a table like this.

Any ideas you can provide in selecting the drive parts would be appreciated.

Thanks,
Brian

Weldtutor, I have been following your build for a while and am getting ready to start my own build.

For your chain drive parts, what size chain and gears did you use to work with the 60:1 reducers?

Any ideas you can provide in selecting the drive parts would be appreciated.

Thanks,
Brian

Hi Brian, thanks for your interest.

My build uses #40 roller chain, & 3" diameter sprockets with weld on hubs of the size to fit the speed reducers output shafts.

My servo motors specification is 4000 R.P.M. so a larger than usual reduction was needed to achieve the suitable speed range for plasma cutting.

You might try agricultural or farm equipment suppliers as a source for the gear boxes similar to what I used if you go that route. Backlash is not an issue with the components I used for my machine & its' application.

The Plazpak system is quite popular. Motors used with that package would not likely need the speed reduction that I required. Timing belts & pulleys might be a more economical & suitable speed reduction system. Tom at CandCNC would no doubt help you to determine your requirements if you go with his motors & controls.

I wish you well with your project.:)

Everything looks awesome, guys.

I built a table as well (I started a thread showing pictures, etc.) but am having issues with it. The electronics are no problem for me, same for mechanics. My biggest issue is how to get what I have on paper into QCad or GCam or EMC. Or onto the computer, for that matter. I can scan in a sketch but it is pretty crappy when I try to spew out a DXF.

Any ideas?

I can scan in a sketch but it is pretty crappy when I try to spew out a DXF.
Any ideas?

Most people would echo your "pretty crappy" remark when attempting to scan or auto-trace drawings that are converted to DXFs.
In many instances the clean-up time is greater than making a new drawing.

The DXF files that I have created or modified have been done using progeCad 2008 Smart (free from various sources) or it's earlier version from 2006.
Most art files can be created with a series of arcs & lines.

CAD programs certainly can be challenging to gain proficiency.:(
Be patient, play, experiment & you will learn.

Open segments in a drawing used for a CNC can cause problems.

Use of "layers" in a drawing can be beneficial to control cutting sequence for plasma arc projects.

Without a proper DXF a CAM program will not give you a suitable G-code to run.

This is a creature version of a "Gecko" not the fine performing electronic type in my control package.

Lower area of picture shows the item as cut, before forming to give a 3D effect. It is 22" long, from 14 Ga. mild steel.

After forming at top, the body is curved, feet sit flat, eyes project out, tail is 1/2" raised and head 1-1/2" up.

Cool Gecko!
Mike

Thanks Mike.

The electronic controls you put together continue to work well for me.

I have fun drawing, CNC plasma cutting, & finishing these little creatures.

Pictured below is a frog (8" long) that was created using a technique similar to that for making the gecko shown in the earlier post.

Hi Weldtutor,

Quick Question.

Do you think your design would work with a router head?
I love your simple yet very effective design but I want to be able to cut wood also...

Thanks
Ronan

Do you think your design would work with a router head?
I love your simple yet very effective design ...

Thanks for your interest.

Yes, this design would work well for a router. In planning my plasma table I noticed several others here at CNC Zone had used a similar method for routing. It certainly works well for my application.

Posts #13 & 14 show how the Y axis has an "anti lift" bearing beneath the top guide rail to compensate for the mechanical forces when routing.

Another approach would be to have the lower Y axis bearings below the guide rail, leaving those at the top above the rails there. The 2 guide rails would then effectively be "captured."

The only one I've ever mounted on my wall.:)

The share your files forum has a DXF for this deer head.

These butterflies were all cut on the plasma table in this project log.

Sizes range from 6" to 18".

That is some real nice butterflies Weldtutor. Would you share the dxf or g code for any of them. It would be nice to see what it took to get the shapes and try and duplicate them for my wifes flower bed.

Thanks
John

It would be nice to see what it took to get the shapes and try and duplicate them for my wifes flower bed.

Thanks
John

Thanks John,

I had fun with them.

The first one in each row are my creations

The other four are from purchased commercial files.

The first ship pictured is 14" X 14". Hammertone black finish.

Tall ship is 16" X 18". Flat black enamel.

Both are cut from 16 ga. steel.

Those are looking good. I'm almost finished with the updates on my plasma table as soon as I'm done I'll test my butterflies and then upload the dxf files.

John