How would you compare the accuracy on the Desktop, Buddy and PRS?

[wespor]

I created a thread in the Buddy forum a couple weeks ago asking about spindles, it morphed into a desktop vs buddy vs full size discussion and while I got a lot of good feedback there, the more the better.

I need accuracy (for carving stamps for leather embossing, printmaking and fabric dying) and z height (for creating concrete molds). The more of both the better but it seems like i'm at an either/or crossroad.

[coryatjohn]

What about speed? Is that a factor?

[wespor]

What about speed? Is that a factor?

I don't think it would be, as long as it can cut the detail and the stamp is durable. My hydraulic clicker is my main fabrication tool, the router will only be used to make tools. Same with my concrete casting, I only use the initial mold to make a urethane rubber mold that I then reuse to cast concrete.

[Ajcoholic]

I created a thread in the Buddy forum a couple weeks ago asking about spindles, it morphed into a desktop vs buddy vs full size discussion and while I got a lot of good feedback there, the more the better.

I need accuracy (for carving stamps for leather embossing, printmaking and fabric dying) and z height (for creating concrete molds). The more of both the better but it seems like i'm at an either/or crossroad.

All Alpha machines have step resolution of 0.0004", while standard machines have resolution of 0.0006".

But ALL the machines have positional accuracy of 0.002".

So to answer your question, the desktop, buddy or gantry machines should all be equally as accurate.

[dana_swift]

Andrew has stated my position- the machine is able to do 0.002". Is the operator? Technique really matters, no machine will get 1" accuracy if the material is not held down.

My question is how accurate is the operator? A new CNC operator will not get high accuracies any more than a beginning manual machinist. Setup, skill, & experience are the key factors if both precision and accuracy are required. It is not automatic with any brand of machine, or product line.

Have you determined your error budget for each step in the process? Its like the old saying: "measure it with a micrometer, mark it with caulk, cut it with an axe".

Setup of the machine matters. How tight to you keep it? How often do you tighten the gears? keep track of the backlash? Check the squareness? Use fresh bits for each cut? How much dust is allowed to settle on the table? How much variation is there in the density of the stock? These things in the hands of the operator, not the vendor.

If 0.1" is your finished precision need you will find it easy to get. 0.01" is not difficult but requires attention to detail. 0.001" requires finesse, setup, calibration, meticulous cleaning, and advanced technique. ShopBot doesn't claim to be able to reach 0.001". However it is possible with some materials and setups.

Most of us on the forum are machine owners who make things. Our customers are usually not on the forum. Each of us has our unique use of the machine and our own expectations and standards. We dont represent ShopBot. We like their products, and most of us have found they exceed our requirements. For your application, consider going to Durham and have them show you what is possible with your specific needs, space constraints, and budget. Talk to them about the maintainence requirements to maintain your precision needs. They can give you the best answers.

Sorry if the forum digresses. We are just humans taking a break from the real work that pays the bills.

Best wishes!

D

[coryatjohn]

>> consider going to Durham

I think this is excellent advice. I learned more in a weekend in Durham than I could have in months of breaking bits by myself.

[wespor]

Thank you, that helps. I guess I got a little confused about the individual shopbot specs. I read that the Desktop's resolution is .00025” compared to .015” with the larger models. I just don't have a really big grasp on how much of a difference that makes or just how resolution relates to accuracy.

I'm expecting a learning curve on the amount of accuracy I can get as the operator, I just need to know I can get there one day with the equipment I've purchased otherwise I've wasted a lot of money.

[dana_swift]

"compared to .015” with the larger models." Where do you get that value? The largest gantry machine they make is specified:

Step resolution of .0004”.
Positional accuracy of +/- .002”.

That is copied from http://shopbottools.com/mProducts/prSalpha.htm That is for their largest gantry router. A buddy is also an Alpha and has the same specs. My personal experience is that the a buddy "can" be better than they specify. My experience with gantry machines is it preforms exactly as they specify. I dont own a gantry machine, but I have worked with several of them.

I dont see any links to the standard models anymore. Is SB no longer offering them?

(Side note, I see that the SB site now requires google snoop ware: "ajax.googleapis.com" and "google-analytics.com" for the site to operate correctly. My browser has those disabled, and others, due to my concerns about snooping especially google. Also required loads are "typekit.com" and "feedburner.com". I really wish sites were not linked to snoopers, especially ShopBot. End of side note)

As to your question about resolution. That is the linear distance represented by a single micro step of the drive motors. A single micro step may or may not overcome the inherent friction of the rollers and result in any motion at all. ( How clean and lubricated are you going to keep your machine?) What will happen with a microstep is a force builds up. After several micro steps the force overcomes friction and the machine moves a tiny bit. How far will it move before friction holds it in a new position with some residual force? All machines do this. All brands do this. Physics is the law.

What the accuracy spec tells you is they guarantee that the force balance details, micro-stepping, vrollers, track hardness, backlash and other engineering factors combined result in a measured 0.002" position accuracy.

Only the best musicians can get the best results from a Stradivarius. Same thing with other tools. The best operators get the best results.

I understand the fear that it wont work out and be misused money. That can happen of course. The machine costs many thousands. A trip to Durham costs much less and makes cheap insurance. Most of the forum users only have access to one type of machine. Asking the typical user to compare them is not realistic. What we all can attest, is that they really work like the good folks at Durham say they do. Not only that but they have the worlds best tech support after the sale.

Get one and start learning. Paralysis by analysis was a problem that held me up too long Know that your results after two years of continuous use will be better than the results after two weeks of continuous use.

Just like violins.


D

[wespor]

"compared to .015” with the larger models." Where do you get that value?

It was the answer I received from SB support via email.

Question: I'm interested in detailed work, namely wood and corian block stamps for embossing leather and printing on fabric. What is the smallest bit your machines handle and are both the desktop and buddy systems equally equipped for detail work?

Those two machines are not equal in resolution. The Desktop model is by far the best for your application. It’s resolution is .00025” compared to .015” with the larger models.

A spindle has an ER20 collet and comes with the smallest as 1/8”. That said, you may be able to find a “sleeve” that could be inserted to hold a smaller diameter.

That is what really started my "paralysis by analysis" as you called it. The need for more cutting space and z height but the fear that accuracy would suffer to greatly. I will buy a ShopBot, probably the Desktop w/ spindle to stay on the safe side since I could potentially buy a BT/PRS with router down the road for larger, less accuracy work. That seems like a waste though if the difference in detail work is minute between the machines.

Here are some examples of the kind of stamps I need to carve.

[jerry_stanek]

What size is the Wharton stamp?