Buying CNC Equipment for Woodcarving

A woodworker gets advice on the pitfalls awaiting the unwary buyer of CNC gear. July 21, 2006

Question
I want to deeply incise 5/4 and 6/4 walnut slabs to produce a unique product. CNC carving is the only way. Am I just kidding myself by looking at the lighter duty tables with the 3 HP routers? The price looks right, but what kind of problems am I looking at, other than slower production times? Some of the cuts may be over an inch deep into the walnut. Will there be deflection problems and rapid wear out of parts and the like on these light duty tables? Not enough software power for the carving? Other problems I might not even be aware of? One option I am considering is purchasing a used higher end machine instead. Am I setting myself up for software nightmares with these old machines when applying Artcam type designs for cutting?

Forum Responses
(CNC Forum)
From contributor A:
The last of your considerations may be the most feasible. I caution you to approach purchasing a used piece of machinery in the same manner you would a used automobile. Know what you’re buying, know who you’re buying it from, and ask multitudes of questions. If possible visit the machinery on site if under power. If you are already committed to using a particular software (such as Artcam) then make sure a post exists for the machinery you intend to purchase. Make sure the era of the controller does not limit you by its ability to interpret or process large code files (if you believe them to be large). There are numerous considerations; do not hesitate to explore them all until you are satisfied. That said, there are some great buys out there if you know where to look, know what you’re looking for and the right questions to ask.


From contributor B:
I bought a 10 year old SCM big 6.5 ton CNC 10HP multiple tool changer, drill block etc. I was told all was in order but that proved to be wrong, however I have now repaired all the items that were a problem, including rebuilding the spindle myself. I am a mechanical engineer, so it was not a big deal. I also replaced chips on the DNC board and now the unit is a dream. I do a lot of deep carving using Mastercam art (currently battling to get a 10mm ball and strait cutter to machine 105mm deep). I do not think you will have any drama with a post as long as you buy a machine with a good controller, mine is a NUM and the guys at NUM USA have been fantastic.

All of the programs I run are up to and bigger than 3 megabytes (300,000 lines of code) and as long as the DNC link is good you will be able to drip feed. It would be worth to check the controller options on this forum when you find a machine that you think meets your expectations. I am glad I did not buy one of the new light, no tool, change machines, because I now see the reason there are auto tool changers and decent horsepower spindles, good vacuum tables and all the frills you can get on a used machine. The message is do your research as to what can go wrong with the machine you intend on buying.

If you already have Artcam Pro talk to your reseller when you are ready to commit and get him/her involved from the get go, as they generally have good industry experience, and can save you a bundle. Before I forget, barter the prices way down - you will be surprised how low a lot of the sellers go. Attend auctions - I saw a 6 month old Morbidelli go for $85K and the selling dealer said the customer had paid $170K - so there are bargains to be had. Don't forget to put about 20 grand aside for tooling. If you think I am joking wait and be surprised - collets, cutters, etc. are not cheap when you need to retool a complete machine.


From contributor C:

Is this your first venture into CNC? Are you a mechanical engineer? Can you afford to hire this expertise or learn the craft yourself before you are up to full production? Buying used can be a great value, especially if you are purchasing a duplicate machine or one you have already run.

Learning from scratch and learning what is not right with your used machine can be an expensive and long learning curve. There are a number of new machines that would accomplish your task with the added advantages of a new machine purchase including controller training, a 1 or 2 year warrantee on parts and labor, hands-on advice about software, tooling and jigging your project. Don't be seduced by low prices alone. Look at your whole project and buy accordingly.


From contributor D:
What will your production schedule be like - 3 a day? 30 a day? A rough out program is not a fraction of the size of a finish run. Each one of those roughing cuts can only be 1/4" deep if need be. Then you only have 1/32" to take off for the finish, and maybe in both directions if you want for a cleaner cut. You can make this 3 or 4 files if you don't have high production rates. With that being the case, something like the Shop-Bot will work out just fine. Depending on the size of the carving, good ball screws will limit backlash and make for better work. If the carving is only something like in a 10" diameter area, high speed travel is not that important either. A little more description of your work will get you some better advice.

From the original questioner:
I plan on cutting a 3d sports motif, say in an 8 inch circle, then cutting in a mounting area for piece of paper on the same piece of wood and some lettering. Yes, 3 or so of these items a day would be what I would expect, plus some prototyping for the next great idea. I have looked at the ShopBot a little, and I am also looking at the Dyna CNC. My Porter Cable 3-1/4 hp router seems to have plenty of spunk when I am tongue and grooving flooring. Your answer about multiple cuts seems to make sense. Do you do this on a regular basis? Seems like there is some storage limitations on the lines of G code - is that a PC storage problem or a controller storage problem or have I missed the point? I have geospatial analysis experience on pc, but I know making a pretty 3d picture is one thing, and making it appear in a solid surface on a piece of hardwood lumber seems like quite another thing.

From contributor E:
I would like a tool changer for doing this kind of work, otherwise you will need to manually change bits, which could be a nuisance if you don't set things up smoothly.

From contributor A:
Consider the following:

1. If you can find a good, reputable used machinery purchase, putting into place, an upper end machine for the same or equal monetary value as a new lower end machine. If things do not pan out for you, you have a much greater chance or recovering more of your investment.

2. If you are purchasing this on a hobbyist level or with the intent of using the purchase for the rest of its life in your garage, basement - progressing to a point of some form of subcontract manufacturing, by all means purchase within your means to accomplish the task you want.

3. If your goals are already with the intent of production, or imminent visions of ramped up production at some date in the future, you’re slighting yourself if you exclude options. I am not a salesman - I offer contributions in this and other CNC related forums at the expense of my own personal time in an effort to try to help people. My hope is that at a minimum you can make educated decisions that you are content with and reflect your best interests.


From contributor C:
Any amount spent on automation should be in the context of the whole picture of what the original questioner wants to accomplish.

From contributor F:
I have one of those machines. It's a Cam Tech Z7, 102" by 52" table. It's not a production machine, it is simply there to add value to my products - carved doors, signs, templates for other shops, inlays, carved kitchen doors, etc. I look at it as another woodworking machine, it's a sliding panel saw, panel router, louver groover, morticer, etc. It is cheaper than all the machines it could replace.

From contributor C:
First and foremost, trying to learn both software and machine operation at the same time is a recipe for high stress burn out. Second, and unfortunately, the over-selling of software for a particular application is common. Much consternation can be avoided by looking critically at your expectations and how those expectations will be met. A good salesman will give you the information you need to make an informed decision. I suggest that you get your actual product designed and make some sawdust. If the experts can't easily reproduce your work, you can't expect to be able to do it on your own. If you are making a prototype for production, expect to pay for their time, but at least you will know it can be done. There are pitfalls, but they can be managed.
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