z-axis resonance

[scottp55]

Jut, I'm a stay at home now and don't really need one (don't Twit or Text either), but in my traveling days(95-98) did have a Motorola 3W bag phone as big as a Boston phone book (and the 600-1,000 a month bills to go along with it) People used to gawk at while they were checking their alpha-numeric pagers. Watched Jon's vid again up til 13:20 and that's what mine sounds like. Didn't notice anything loud-sounded smooth as silk. You got to remember he hadn't used it in a year and also was Using Australian power for the first time, so maybe his cut speed had to be tweaked from his Canadian speeds? Our 2 sound like when he did his Z-zero routine. Don't think you'll find a better machine at the price that does what the Desktop does(hard to imagine at ANY price). See if you can have someone do a Demo for you so you can put your mind at ease. Not a bad idea to call Shopbot and see if anybody is close and also get a taste of what the company is like, as it's as good as their machines or better--it should be a huge part of decision in buying a machine anyways. Good luck!

[Brady Watson]

I'll say again, all CNCs with steppers show resonance at certain speeds. The speeds set in the 2nd video you show are set at about 36 Inches Per Minute or 15mm/sec; .59 In/sec - which is probably about the speed that tool makes resonance.

I'm not sure what you are really asking or what answer you are looking for with this post. The machine makes some noise at certain speeds. So what? $5k is nothing in CNC Land. The only way to 100% get rid of MBR is to buy a tool with servos...and that is well over 2x the cost of this machine. It won't make you any more money any faster than a stepper machine will, so perhaps earmuffs are the solution. Yes it is an ugly sound. We all get it. But don't throw the baby out with the bathwater.

It is possible and probable that the machines you saw need to have their Z driver trimpot adjusted to squelch some of that resonance. These are fantastic little machines for the money. Don't let a little motor noise throw you off. Go visit a shop that has one & test the Z at different speeds so that you can get a first hand understanding - (and probably throw your hands up saying, "Oh, that's all that was?")

-B

[Billions]

Hey Jut. I understand your concerns - I am actually running a Shopbot Desktop in my apartment! These are expensive machines (I think so anyway) and a while sound like that may seem like a byproduct of cheap construction or something, rest assured if you're concerned about quality and if your investment will be sound, there's nothing I've found lacking quality in my two Shopbots.


I went with the spindle version of the Desktop, which is the one shown in each of the videos you cite. I also have a Shopbot Buddy in my studio. It's has a router instead of the spindle.

I mention it because I would say that's the single biggest difference in sound level generated in the the two systems I have, along with your dust collection system - the spindle being quieter than the router. Of course you have to pay more for the spindle.

The sound you point out is strange and not something you ordinarily hear when using one of these machines. Occasionally it happens, though. Sometimes I've gotten what I have to assume is a USB connection stutter that causes a noisy, jerky-jerky move from the Buddy machine but it's very rare and passes quickly - seemed to be a result of me having my jogging speed set too high. Cutting is another story, as sound can vary widely on the bit, speed, and density of the material.

I think the rest of the time in those videos is far more indicative of what you'd be getting overall.

Good luck with your decisions. I just wanted to chime in and assure you that a sounds like that are far and few-between and that even high-quality machines like this sometimes make odd noises.

[Max Girouard]

He slowed down the z-axis later in the video and it still sounded pretty bad.

What I'm trying to get at is whether or not this amount of noise is normal for a shopbot. Scottp indicates it's abnormal. I found another youtube video where it's much quieter:
https://www.youtube.com/watch?v=0dKcuvh35m8#t=428

I'm not going to roll the dice on another machine. I want to be 100% sure this machine does not shriek. That would indicate quality control issues on shopbot's part.

Before passing judgment on the quality control of a shop bot you may want to look a little further into how a stepper motor works.

http://www.haydonkerk.com/Resources/...2/Default.aspx

As Brady mentioned earlier, any stepper motor will have a speed at which its resonance will be noticeably different. If it is too loud for you, just change the speed that the stepper is moving and you will be fine. My Z makes a louder noise at lower speeds but I haven't been bothered enough by it to change the speeds.

[scottp55]

Thanks for that Max. I understood what, but never why

[that1guy]

Hey Jut. I understand your concerns - I am actually running a Shopbot Desktop in my apartment! These are expensive machines (I think so anyway) and a while sound like that may seem like a byproduct of cheap construction or something, rest assured if you're concerned about quality and if your investment will be sound, there's nothing I've found lacking quality in my two Shopbots.


I went with the spindle version of the Desktop, which is the one shown in each of the videos you cite. I also have a Shopbot Buddy in my studio. It's has a router instead of the spindle.

I mention it because I would say that's the single biggest difference in sound level generated in the the two systems I have, along with your dust collection system - the spindle being quieter than the router. Of course you have to pay more for the spindle.

The sound you point out is strange and not something you ordinarily hear when using one of these machines. Occasionally it happens, though. Sometimes I've gotten what I have to assume is a USB connection stutter that causes a noisy, jerky-jerky move from the Buddy machine but it's very rare and passes quickly - seemed to be a result of me having my jogging speed set too high. Cutting is another story, as sound can vary widely on the bit, speed, and density of the material.

I think the rest of the time in those videos is far more indicative of what you'd be getting overall.

Good luck with your decisions. I just wanted to chime in and assure you that a sounds like that are far and few-between and that even high-quality machines like this sometimes make odd noises.

Thanks for the feedback Billions. Yes, by and large this machine and shopbot is a good company - i have no doubt about that given all the things people are saying on this forum and youtube reviews. I am a perfectionist and want the machine to work near flawlessly, especially given it's high price tag. But I think this little resonance issue is something I can get over, given all the other good qualities.

[that1guy]

Before passing judgment on the quality control of a shop bot you may want to look a little further into how a stepper motor works.

http://www.haydonkerk.com/Resources/...2/Default.aspx

As Brady mentioned earlier, any stepper motor will have a speed at which its resonance will be noticeably different. If it is too loud for you, just change the speed that the stepper is moving and you will be fine. My Z makes a louder noise at lower speeds but I haven't been bothered enough by it to change the speeds.

Yes I'm aware of stepper motor resonance. But it's NOT only stepper motors that resonant or make noise - the machine itself can resonant. If the rails are not perfectly aligned that will cause resonance of the machine. My small desktop cnc machine has this issue.

My concern was hearing this resonance at different z axis speeds. In those youtube videos I linked, the z axis is making funky sounds at different speeds. It seemed like a red flag to me. How can the x and y axis be silky smooth but the z axis be so noisy? Perhaps I'm being too critical, but I want a machine that runs smooth, especially at this price point. As someone said, I shouldn't through the baby out w/the bath water - and I would still probably order the machine even though it's got this (potential) flaw.

[gc3]

this outta drive you crazy...

https://www.youtube.com/watch?v=7kcmkOaBguA

[that1guy]

I'll say again, all CNCs with steppers show resonance at certain speeds. The speeds set in the 2nd video you show are set at about 36 Inches Per Minute or 15mm/sec; .59 In/sec - which is probably about the speed that tool makes resonance.

I'm not sure what you are really asking or what answer you are looking for with this post. The machine makes some noise at certain speeds. So what? $5k is nothing in CNC Land. The only way to 100% get rid of MBR is to buy a tool with servos...and that is well over 2x the cost of this machine. It won't make you any more money any faster than a stepper machine will, so perhaps earmuffs are the solution. Yes it is an ugly sound. We all get it. But don't throw the baby out with the bathwater.

It is possible and probable that the machines you saw need to have their Z driver trimpot adjusted to squelch some of that resonance. These are fantastic little machines for the money. Don't let a little motor noise throw you off. Go visit a shop that has one & test the Z at different speeds so that you can get a first hand understanding - (and probably throw your hands up saying, "Oh, that's all that was?")

-B

Thanks for the feedback Brady. I was hoping to find out if this noise is common to all desktop machines and whether folks thought it was a problem. Seems like most people don't care.

I think the shopbot desktop is priced pretty high. Compare it to the Tormach PCNC770 (not really a desktop machine, much heavier) is slightly more expensive and runs smooth as butter.
http://www.tormach.com/product_pcnc_...html#techspecs

[Brady Watson]

I think the shopbot desktop is priced pretty high. Compare it to the Tormach PCNC770 (not really a desktop machine, much heavier) is slightly more expensive and runs smooth as butter.
http://www.tormach.com/product_pcnc_...html#techspecs

Both are good machines. However, it is not an apples to apples comparison. The SB is a router & the Tormach is a milling machine. Two very different machines made for different work, even though they move the cutting head in similar ways.

If you really need a CNC, you don't want to shop on price. Get something that will do what you need for your type of work. If you just want to have one, well I can't advise you on that other than to say the Desktop holds its value well. My first ShopBot was nearly $30k back in 2001 - which is a lot more than $30k in today's money. I made that money back quickly because I shopped on value and not price, and matched the tool to the work I was doing. In fact, I've owned 7 ShopBots over the years, including my newest one, the Desktop. These tools make money, as long as you have the capacity to feed it work.

With all things being relative, a $5k machine is in no way 'expensive'. It isn't an appliance you'd buy in a retail store; but it is something that you can use to make money with. Your return on investment can be very quick, if your plan your work & work your plan. It should be considered an investment...not just a casual purchase.

Another option you may not have considered is to join a 'Maker Space' etc and 'rent' time on a ShopBot or Tormach and try before you buy. At the very least, I recommend contacting ShopBot and ask them who in your area can demonstrate their ShopBot to you so that you can really see one in person & get answers to all of your questions.

-B