Question-What to look for in a used CNC?

[Rob Damon]

Quick questions.

I was considering a hobby grade CNC (like the Shark Pro or that range).

Recently there have been a few of the production level CNC showing up locally online, for quite a bit more, but I could probably swing the added cost.

For example:

"ShopBot PRT Alpha 48 x 96 cnc router with 3hp columbo spindle...Machine runs great and has been very reliable over the past couple of years. Used in a Cabinet Shop."

If I were to go with a used CNC router, like this, what types of things should I look for that are "warning" signs?

What type of questions should I ask about the unit or visually inspect?

If the unit is more than 5 years old?, 10 years old?, would it still be worth looking at?

I know the first question for me is "what are you going to use it for?"
The answer is "for retirement hobby use."

I have a 200amp dedicated electrical service to a 1200 Square foot shop, 5 hp cyclone, and can easily deal with an 1 ph to 3 ph. converter to run the CNC if it is wired for 3 phase. So these would not be issues.

Thanks for any suggestions,

Rob, Yorktown,VA

[james mcgrew]

a prt is a good buy and all of the parts are basically replaceable!! the shopbot also has been on the market a long time so there are plenty of them out there and there are good buys to be had. if you are gonna spend 3-4500 on a shark (used ones mean someone is not happy or can not figure it out or is buying a larger cnc because they learned about size limitation) then go a little further and look for the used bot, (there are very few if any camasters ever sold by there owners) you will come to appreciate the size ability of the 4x8,

i bought my first cnc used and told myself if i had to spend 4-5000 to upgrade or repair it would it still be worth it when the answer was yes then i bought it and while it worked great i did upgrade it a bit at a time over the following year and sold it for what i had in it, but not until i had bought a new one!

ps both camaster and shopbot have table tops under 5000.00 coming soon!!

jim

[Roger Kirkpatrick]

Something to look at would be the rails.
See if they still have a sharp V or are they dull and mushrooming down.
If they are consistent the whole length it may be O.K. but if they are worn in 1 area you may have to replace them.
If the VFD for the spindle is 3phase input sell it and buy 1 that can take 1 phase in and power the spindle with 3 phase.

[Rob Damon]

Thank guys. This gives me a starting point.

Rob

[John McClanahan]

Be sure it comes with all hardware and software needed to make it run. Most hobby machines run off of the PC's printer port, controlled by software like Mach 3. Bigger machines may use a special software and interface card in the computer. Make sure the software is transferable, or you at least know what you are in for if you need to buy some.

In my day job I see used computer controlled equipment that has little value because the controller computer and software was separated at some point.

John

[Roger Kirkpatrick]

Control software is free and on the ShopBot web-site for download.
They post all updates as they become available.

[james mcgrew]

i purchased my first cnc (CAMaster) in 07 it was built in 99 and determined that with the dos controller and 1/2 step motors (it was built to cut sign letters and still did that really well) it also had "v bearing rails, the same type shopbot still uses on thier machines (camaster has since moved on to encapsulated Hiwins) the v bearings are what has been mentioned as being prone to wear, so with the need to upgrade controller, motors and potentially the rails and bearings (est cost on camaster $4500) i offered 50% of new as the price. the company no longer used the machine and it had done its accounting depreciation for them so i purchased it. in my case the rails were fine, a sign company cuts slow for non welding of materials and had done no 3d work. the motors and drives were excellent as well but i wanted to upgrade to the wincnc full gcode and non propietary uses so there would be no limitations, (i will not own a machine i cannot change parts on myself.) if this machine had been in a cabinetshop i would have offered less as the wear from nesting wood is far greater than softer signmaking substrates. the machine i purchased was a good one (i bought a new camaster in 08) and i sold it for all i had in it as it was fully new (other than the frame) i f it is a bot find a local fellow who owns one similar and ask him to look at it the savings could be profitable!!

jim

[Rob Damon]

Here was one that I am looking at. There are two others, but I don't have specific info. on them yet.


========================================
ShopBot Specs: PRT Alpha 46 x 98
- Single Phase Power - Takes a double 30 amp 240 volt breaker and one single 30 amp 120 volt breaker
- Has a 3hp Colombo spindle-
- Has (4) Vexta DC gear motors for the x,y, & z movements....
- Runs off of a standard pc
- Comes with the partwizard software cd that came with the machine when we purchased it
- Machine is aprox. 4 years old
- We generally used the router to cut plywood and hardwood cabinet components
- Has two control boxes that are mounted to a wall, one main control box that is hooked into the panel box and into the computer through a simple usb connection, the other control box is a control for the spindle motor...
- Does not have the vacuum for material holding
-Asking $7500
===============================================

Thanks for any observations, opinions.

Rob

[Guy Mathews]

BUY IT! Even if the rails are worn, you can get replacment railing and V groove rollers from McMaster Carr.

My Machine was much older and I sold it for a lot more then what these people are asking.

The great thing about this ShopBots is the fact that all of the hardware is in the control box.

If the machine comes with the original disk, you will be able to install the firmware on any laptop with USB.

Shopbot also has great support.

$7500 for this machine is a steal!

Guy

[james mcgrew]

here is an alpha!! for the same price

jim

[Rob Damon]

James, It's the same one! That's the guy I have been corresponding with.

Guy, it comes with the software.


Rob

[james mcgrew]

4 year old alpha at 7500.oo buy it !! i am surprised it has not sold, the alpha means it is closed loop stepper and that is the top setup for shopbot, hang if i wasn't ready to have another built i would buy it

jim

[Keith Outten]

Rob,

Thats an excellent deal if the spindle is in good shape. The problem with spindles is that some people don't go through the warm-up procedure and the ceramic bearings will wear prematurely. I don't know what the cost is to rebuild one, most people send them to a shop to have the job done. The brave ones rebuild their own spindles
.

[Guy Mathews]

James, It's the same one! That's the guy I have been corresponding with.

Guy, it comes with the software.


Rob

BUY IT!

As for spindle, 2 years ago we purchased a second spindle for the ShopBot directly from PDS. It was a 5HP Colombo Spindle and we paid 2200 dollars. They wanted 1100 to rebuild.

I recently took 3 of our spindles from our 10 spindle machine up to SPS Spindle Repair in New Hampshire. The cost to repair was over 20K. Part of that cost was to learn how to rebuild the spindles.

The bearings are the expensive part and in the case of our 10 Spindle machine, the drawbars are also quite expensive. The spindles themselves are quite easy to work on. The bearings need to be loaded properly, that is the big secret that no one will tell you. Once you know that, it is just a systematic breakdown and reassembly. If parts are worn, then plating and grinding come into play and need to be done by a qualified machinist. However, as I explained to the boys at SPS, I work with WOOD not NASA so the tolerances that they were wanting to achieve on our spindles were ridiculous. They still did a first rate aviation industry standard on our repairs, however, future repairs will involve replacing the draw bars and bearings as needed. Plating and grinding will go out the window unless I start milling parts for NASA which I highly doubt.

Bottomline, BUY THAT SHOPBOT!!!!!!!