The Importance of Tuning Up CNC Equipment

      Low end or high end machines, performance and accuracy depend largely on "polishing" the setup. December 10, 2007

Question
I'd like feedback from people who own a Shopbot or have run one. I am considering buying the new Alpha 5x10 model. I don't care if it is not the fastest machine out there, all I am concerned with is that it produces a quality cut and it's accurate. I will trade the slower cut for the lower cost, but not the quality. I am primarily cutting cabinet case parts out of 3/4" plywood.

Forum Responses
(CNC Forum)
From contributor E:
First, ask at their website - they are some of the friendliest people on earth. They will answer any question and there are hundreds doing just what you want to do. My guess is there is someone close to you that would be more than happy to show you in person how it runs if you just ask on their forum.

Second, if you are going to buy any machine, you need to go to the upcoming tool show in Las Vegas and see the machines run right in front of you. Remember to ask a lot of questions and remember the salesmen are trying to sell you their machine. I don't own a Shopbot, but have run one. It's a good machine for the money. If you look into the upgrades they offer, it can be a great machine.

Third, look real hard at the software/design ware you will be using. There is a very hard learning curve at first. I have never regretted getting my CNC machine and it has allowed me to do things quicker, cleaner, and better than I could the old way. And I didn't buy big iron to do it.



From contributor I:
I've been running one for six years now. Currently upgraded to a PRT Alpha. This machine, for the money, has been a true workhorse. Some years we've pumped out as many as 40,000 parts for furniture. On the few occasions I've been down, the company has bent over backward to get me up and running again.

While it is what it is, a low-end CNC machine, it has been far more profitable for our situation than many more expensive machines would have been. Would I like to move up to a more rigid and faster machine? Yes, but for now it does not make good business sense to do so. It makes the parts we need at tolerances we need as fast as we need and the machine paid for itself after the first year.

Their forum is also an excellent source of information and support. I'd check it out and see what you think.

One thing to remember is that the machine alone is not everything. It is a package consisting of the basic machine, the spindle, hold down method, tooling and software. Any one of these can cause you serious headaches if not addressed. When all well put together, though, they can really improve your production and bottom line no matter what make you end up with.

The factory will also hook you up with a user in your area. Hopefully with a user who actually knows how to really maximize the use of his machine.



From the original questioner:
What I am really interested in eliminating is some of my duties on the shop floor, in particular cutting the jobs. I have not found anyone in almost 10 years who can do it as fast or accurate as I can. We are already using Cabinet Vision software to design our jobs and produce cut lists. I am really interested in accuracy and quality of cut. I was recently at a shop where an Omnitech was running. The cut was not good and the case was not clean. I'm not paying 60K for that!

Contributor I, you mentioned you would like to upgrade. Is that primarily for speed? Or are there things you can't do?



From contributor I:
As for speed, I'm cutting at around 500" per minute. There are faster machines out there, but when you start doing nests of small parts, all the slowing for corners doesn't net you that big of a gain. I would like to be able to bid more complex outside cutting jobs. That would require tighter accuracy and a really good tool changer. However, since I've seen a decline in this kind of work in my area, now would not be a good time to move up.

Shopbot runs about .015 on overall accuracy without factoring in tooling flex if running small diameter tools. While that's okay for the work I'm doing, there are tighter machines out there.

For cutting out cabinet parts, it's a pretty good machine. You may have to tweak a few things in your construction methods to avoid a lot of tool changes, but it's also possible to do a tool changer on the Shopbot if you feel you need one.

I think more realistic for me will be to upgrade to their latest drive system in a few months and stay with what I'm doing for the next few years. It is still a very profitable part of my operation and it's consistent! I've had the same issues you mentioned with employees.



From contributor J:
Clean cuts on a CNC have much to do with the tooling, RPM, and feed speeds. It doesn't matter if you're using a $20,000 CNC or a $250,000 CNC, if you use the wrong tooling, or don't keep it sharp, spin it too fast or too slow, and drive it too fast or too slow, you will get a crappy cut. Also, if your vacuum hold-down system is not being maintained properly, your parts will move.

Keys to clean cuts and accurate parts:
- A well-built, accurate machine.
- Tool holders, nuts and collets in good condition (my rule - if you drop a collet or crash a tool, replace the collet).
- Tools should be properly set in the collet/toolholder (and properly torqued with a torque wrench).
- Use the right tool for the cut (i.e. compression tools with long up shears will chip the top of 5/8" and thinner melamine and when cutting dados).
- Don't use dull tools (this is way too common).
- Clean the filters on the vacuum pump regularly.
- Inspect the vanes on the vacuum pump for wear.
- Inspect the vacuum hoses for kinks and holes.
- Make sure the vacuum gasketing under the spoilboard is not flush with the vacuum table (it should be about 1/16" or so above the table to allow for compression).
- Make sure you maintain and service the machine to manufacturer's recommendations.
- Software, post processors and the machine control all must be configured properly to get great results.
- Programs (especially feed and speeds and tool compensation) you output to the machine need to be customized to the parts and materials you are cutting.

I sell Omnitech machines and all of my customers (even those with other brands of CNC machines) get clean, accurate cuts when they follow the recommendations above. When you evaluate CNC machines, be aware that the sales folks will practice and polish a demo (using the steps above). The Omnitech shop you visited needs to polish their operation the same way to realize the efficiency of the CNC. You should also do the same with your machine. The Omnitech (as well as any other CNC) can only perform as well as its operator allows it.



From contributor B:
Contributor J is right on with his advice. The machine you saw running more than likely had setup issues, rather than machine quality issue. Machine wear and tear are also a possible cause of a poor cut, but more then likely, it was the tooling related issues.

I've always been a big fan of ShopBots as entry level machines. If you are thinking about building up one of their machines to $20k or more, though, then you should educate yourself on the similarly priced alternatives. The larger machine manufacturers such as CNT Motion (my CNC), Techno-Isle, Multicam, etc. all have entry level routers. You may decide to stay with ShopBot, but at least see how it compares to similarly priced setups.



From contributor P:
Heard nothing but good things about Shopbot and their people.

Responding to the Omnitech remark, I currently own the Selex Mate 4 x 8. I went to this machine from a Multicam. This machine has run 40 hours per week for 9 months with excellent results. We cut parts for a local upholstery company that supplies a large manufacturer. We are lucky to have this work. I have had great results with my custom cabinets. True test is the frameless cabinet. Always square and very accurate. Tech support great. The machine comes with a Fanuc controller, Andi spindle and 10hp Becker pump. In my opinion, an excellent buy.



From the original questioner:
Thank all of you for your input. It's been helpful. I didn't mean to pick on Omnitech. I'm sure it's a good machine. My point was that I wouldn't want to spend that kind of money on any machine and get poor results.


From contributor L:
I'd bet the shop getting poor cuts on their Omnitech doesn't know or doesn't care. Cut quality is 99% about the proper tooling, speeds, and feeds.



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