Hi All,
This is just a quick warning for newbies who might be considering purchase of a Practical CNC. In a word, "Don't."
I made the mistake of buying one and in five months it never worked right. I spent hundreds of dollars shipping parts to Practical for repair/replacement. I had a controller burn out, three motor failures, and four driver failures and a bent X axis shaft. Their expensive torch control system never did work right and slammed my new torch through a sheet of steel doing considerable damage.
I replaced the Practical CNC torch height control system (which didn't work) with the MP-1000 THC system from CandCNC (which works great). Practical CNC then used that as an excuse for denying warranty service on the controller. Please note that the controller and torch height control are separate things.
Anyway, in desperation, I finally bought a prototype controller from Tom Caudle at CandCNC. Now everthing is working great. Tom gives fantastic service and his advice is a tremendous help. Need help? Ask Tom on this site or on the CandCNC Yahoo group.
I use Corel Draw and ProgeCAD Lt (ProgeCAD Lt is free) for my design work, SheetCAM for layout and to generate GCode, Mach3 as the controller software, PSC-650 power supply and controller, and the MP-1000 THC system. Now I have a system that works pretty damned well. And Tom has become a friend. I wish that all businesses were run by his principles.
I hope this helps some people to avoid the mistakes I made by choosing Practical CNC.
Paul "Graybeard" Paine

Graybeard,
How long ago did you buy your Practical machine? I bought mine a little over a year ago. Now they are using linear rails on all axis(not on mine though!) Did you get the servo or stepper control?
I also question whether it was a mistake to buy practical but I am making parts with it as a router & a Plasma.
I would recommend anyone who does buy a practical to not buy the practical THC. Although mine does work, you have to baby sit and raise the torch between cuts.
I have the stepper drive and have not had any problemswith them.
My .02
Cutmore

Hi Cutmore,
I got my machine about six months ago. It has the linear rails and servos. It was definitely a mistake to buy from Practical. About the only thing good about it is that I've learned more about CNC tables than I ever wanted to know. The education may be a good thing though since my neighbor wants me to build him a table that works better than the commercial unit he bought for $75,000. We are working on the design right now. We are planning on using the controller and THC system from CandCNC.
Graybeard

Graybeard,
Thanks for the info,I too learned a lot about cnc that I did not know before, like what not to buy! I run a Motionmaster router at work, it has a Fagor control and is great to work with. If pix of their design would help let me know. Who made the one your neighbor bought?
Cutmore

Cutmore,
I think we have the essentials pretty well worked out. We are planning to go as simple as we can on the new machine. My neighbor runs a steel fab shop building natural gas compressors, pressure tanks, and components for oil rigs - on-shore and off-shore. Also does sand blasting and industrial painting. The plasma table he uses now is from Retro-Tech and it works pretty well. It has an 8' x 12' table and he uses it to cut parts up to about 5/8". It can do plasma cutting and oxy/acetylene cutting. He farms out heavier work to a local company and light work to me. The new machine we are planning will also be 8' x 12' and should do material up to about 1.25". The Retro-Tech has nearly paid for itself in the first year by savings on parts cutting. We are hoping a new machine would result in even more savings. By the way, he is accepting requests for quotes if anyone needs big fab work done.
Graybeard

Hey folks I am new to CNC machines so be gentle.

I would like to get a turn key system to do router and plasma work. I was looking at practical but now you guys are scaring me. Who makes a table and controller that someone uses today that they would recomend? Am I going to have to buy the pieces from seperate vendors to get a good machine? If yes then I may see if someone can guide me to the best places to get the parts.

Thanks!
Turbo

Hi Turbo,
If I could afford to do it over again, I would build my own machine in the form of the EZ-Router, using CandCNC controller and torch height control, with good steppers. I'd rely on Tom Caudle (Torchhead) for advice and Mariss at Gecko. run with SheetCAM and Mach3.
Graybeard

you know its funny, i have a practical cnc that has been running for about 6 years now. Its been abused but still works good. I guess is all in what you expect to get out the money that you put into it i guess.

Not all Pintos burned up. Not all Practical's are junk....just some of them. PCNC has had a rollercoaster history of quality control problems, electronics that are marginal and customer service that reads like a horror story.

Example:

Customer: "My table came in and when I turned it on the Z slammed into the grid and blew the 10A fuse on the back. What should I do?"

PCNC "Support Engineer" (his reference not ours): "Ahhh...put in a bigger fuse. Those drives can handle 20A's"

The results from that advice was that Fire shot out of the back of the unit.

If you got a good one then you caught them during an up time. 6 years? You must have one of the first ones they made that uses Flashcut and Gecko's....wait, I don't think Gecko's were around at that point. Better worry because Joe quit using Geckos because they were "defective" In fact he didn't pay for the last 35 pieces he used and refused to return them because they were "evidence". He has a lot of "evidence" from other vendors too since they never got paid for their goods.

I have a mailbox full of PCNC stories. All true and all from their customers or vendors. Want to trade a few?

yep it uses geckos and flashcut, I know the stories about PCNC. Ive read joe's blurbs on the internet. I guess i should be just happy that mine works just fine!

After reading the post which company has good table and support out there without breaking the bank say under $20,000 USD.

Be sure your drives are adequately heatsunk. I heard stories the drives were run without any heatsinking at all. Touch the drives after the machine has been on for about an hour. If they are uncomfortably hot to the touch then it's also uncomfortably hot for the electronics.

Mariss

After reading the post which company has good table and support out there without breaking the bank say under $20,000 USD.

build one yourself

I am rebuilding mine now with Tom's new stuff. I am not unhappy with the basic table because I could get good cuts out of it. The Y drive shaft was never straight (cheap) when it was built, so I am upgrading it and the bearings now. I have found every other consumable (bearings, gears, belts, etc.) from other suppliers. I think it is going to run pretty smooth when done. (plasma only) Even using the top rail and plastic type rollers. (Takes crashing really well too) :)


I was the first one to run SheetCam on my table and had Tom's THC early on. I am now going to Tom's Nema 23 500 OZ stepper setup because my Practical box stopped working. I am not sure but the Z being tight did not help anything. I have that sliding free now. Mariss warned me a while back about the heat sink deal and I have a feeling that might of raised it's ugly head. My table is a three year old 5X10 version. It's pretty strong with all the extra braces I added and when I get it done I expect it to perform as well as it needs too.

I am happy that I will never have to email Joe or any of that group again. That right there is worth more then you know. I guess that would put me in the group of happy Practical owners. :rolleyes:

This is the worst company i have ever dealt with.
I pucrahced and paid in full 7 month's ago and still have not got all the parts in working order.
I purchaced there top of the range machines and it hasent even ran yet.
There unbeatable backup is poor to say the least.
Save yourself the heartake go alsewhere.

Wish I had found CNCZone before I purchased!!!

I am new to the CNC world, I do have twenty one years of AutoCad under my belt, a degree in mech. engineering and a degree in optical engineering. I explored and reviewed a lot of information on five or six different routers. Talked to a E-Z Router owner, but was not impressed with the mechincal design of the machine. I spent several hours with a Practical CNC owner & table before I purchased a 5 x 10 Dual Two in March of 2007, recieved late April 2007.

Did not recieve my tourch adapter or bed, still waiting for those items. No assembly or operating documintation, a video with reference to a machine that did not resemble the machine I recieved. Some vendor documintation with spindel, mistor, wincnc, and bobcad v21.

After assembling we started with G28, and the "Z" plunged into the bed. Bad encoder, this damaged the "Z" drive nut by pulling the s.h.c.s. thru the plastic flange. Practical responed quickly with a new encoder and we were up and running within days. Cut parts for a day when the "X" took off and slammed into the solid stop of the gantry, bending the "X" drive shaft, bad encoder. This time it took a couple days of leaving messages, our frustration set in, we made a new shaft and wedged a plastic shim under the encoder cat five connection and it worked. We recieved a new encoder and drive shaft in a week or so. After replacing parts we managed about forty hours of machining, when the "Z" plunged into the work piece and the servo controller started smoking. The "Z" servo card blew.

After leaving messages for several days, Practical responed with a new servo card and stating they have had problems with servo cards. Machine worked well for a few days when the "Z" plunged into work piece. Stripped "Z" nut! It took two weeks to recieve the part and fifteen minutes to replace. The machine worked for three hours when the "Z" plunged into the worked piece. Hit the e-stop in wincnc and turned off the servo controller. Seconds later, turned on the servo controller and "puff", blew all three servo cards.

After leaving three and four messages a day, five days later, I got through. Sent the controller back, their responce, Practical said the ground shorted due to external power surge or power source. Our machine is isolated from any other equipment or power source. Anyway, to make this long story short, Ive been down four weeks and still waiting for my controller to be returned.

Do not get me wrong, I like the mechincal design of our machine, but the electronics seem to be weak, my weakness as well. Any advise would be helpful.

Thanks for me letting vent.

Best to all!!!!

CaryK

Your experience with Practical CNC is roughly similar to my own. My suggestion: get a new controller and the THC-1000 from CandCNC. Run Sheetcam and Mach3. Tom (Torchhead) got my system working and is one of the greatest fellows you'll ever meet; he's honest, helpful and knowledgeable. Anyway, it worked for me. Now my system works like it should.
Graybeard

Im just telling you that I was lied to by DynaCnc.. I noticed that you did not address that in your response to me. They were sending out a link(and I bet they still do) that showed why there machine was better and showed PracticalCnc using "plastic" parts and such...this was completely false.
Once again just my experience and opinion.

Well, here we are again with another liar! He claims his recent PCNC table has plastic parts and bad electronics. We ALL know that's a lie because AB says it is!

Probably just Dave posting to try and harass poor old PCNC again.....oh, wait....the poster just contacted me and he has a real name, phone number and contact info......:eek:

Tom Caudle
www.CandCNC.com

Wish I had found CNCZone before I purchased!!!

After assembling we started with G28, and the "Z" plunged into the bed. Bad encoder, this damaged the "Z" drive nut by pulling the s.h.c.s. thru the plastic flange. Cut parts for a day when the "X" took off and slammed into the solid stop of the gantry, bending the "X" drive shaft, bad encoder. This time it took a couple days of leaving messages, our frustration set in, we made a new shaft and wedged a plastic shim under the encoder cat five connection and it worked. After replacing parts we managed about forty hours of machining, when the "Z" plunged into the work piece and the servo controller started smoking. The "Z" servo card blew.

After leaving messages for several days, Practical responed with a new servo card and stating they have had problems with servo cards. Machine worked well for a few days when the "Z" plunged into work piece. Stripped "Z" nut! It took two weeks to recieve the part and fifteen minutes to replace. The machine worked for three hours when the "Z" plunged into the worked piece. Hit the e-stop in wincnc and turned off the servo controller. Seconds later, turned on the servo controller and "puff", blew all three servo cards.

After leaving three and four messages a day, five days later, I got through. Sent the controller back, their responce, Practical said the ground shorted due to external power surge or power source. Our machine is isolated from any other equipment or power source. Anyway, to make this long story short, Ive been down four weeks and still waiting for my controller to be returned.


CaryK

I heard somewhere their response was to put in a bigger fuse.... If the control box fire was not big enough.:confused:

I think IMHO the Z axis plunge is their auto bed material clearing tool. I'm sure you could have solved that with the manual up / down button they have.

I remember them blaming Geckodrive back then about their controller problems when I was having controller problems... I guess Rutex now has problems with their servo drives.

Did you say "Plastic Parts". I thought there was a post stating that Dyna was lying about PCNC plastic parts.

When I owned my PracticalCNC table ( sold it, thank God ), It had PLASTIC PARTS. I guess it depends on which day, which dollar, and which parts they have on the given day in which the moon rises in the SW and follows the rain clouds to the east, depending on the sun on any given day ?????? which parts you get or don't get. But hey, that new table advertisement photo looks great! I just can't figure out why anyone would put that in a regular post instead of the new release products forum.(wrong)

But just my thoughts....:)

Wish I had found CNCZone before I purchased!!!

Did not recieve my tourch adapter or bed, still waiting for those items. No assembly or operating documintation, a video with reference to a machine that did not resemble the machine I recieved.

This time it took a couple days of leaving messages, our frustration set in, we made a new shaft and wedged a plastic shim under the encoder cat five connection and it worked. We recieved a new encoder and drive shaft in a week or so.

After leaving messages for several days, ..... It took two weeks to recieve the part and fifteen minutes to replace.

After leaving three and four messages a day, five days later, I got through. Sent the controller back, their responce, Practical said the ground shorted due to external power surge or power source. Our machine is isolated from any other equipment or power source. Anyway, to make this long story short, Ive been down four weeks and still waiting for my controller to be returned.

CaryK

Now IMHO thats "Unlimited Tech Support":)

I doubt that there were actually had two bad encoders. We sell electronic packages with servo interface cards (Differential drivers at the motor and at the Power Controller) and out of hundreds of encoders from US Digital we have absolutely ZERO failures. More likely the heavy shielded cables they use are putting too much strain at the connector. You don't need shielded cables if you use Differential signals and regular UTP (light) network cables will work.

The cables need strain relief to keep them from working loose in the connectors.

If you lose encoder signals for ANY reason you get motor run-away. At that point the control software is no longer in charge and knows nothing about the run away condition. While it's impressive since the rapid rate is roughly 6000 IPM it's also too quick to hit the E-stop and typically results in damage to the Motor drive, the hardware or both.

If the wiring is the same as the unit I saw, all of the drives run off one fuse and they are daisy chained together. There are no electronics to shut down power to the unit if one drive faults. Although the drives are rated at 20A that does not mean without PWM control. If you apply full voltage (wide open) of 60VDC and let it slam into a stop with a 10A fuse it will actually allow about 50A to flow for a few milliseconds. The power FETS see numbers way outside their SOA curves and typically fail shorted. One FET shorts and a few microseconds later the matching bridge FET shorts too.....THEN the fuse blows:(

No (affordable) Servo drive will survive a full speed, wide open crash. Limit switches on the table tied to the power controller (not just the control software) to turn off power to all motors, and dynamic load dump/braking can help, and fusing each drive individually and providing separate ground and + leads to each drive (not daisy chaining) would keep the damage down to one drive.

tomCAUDLE
www.CandCNC.com
BOB's
Digital THCs
DXFTool Software
Complete Electronic Packages
Stepper & Servo Systems
Hand Controllers

Interesting side note on this particular customer. They ordered their table with an expensive Spindle (HSD German 3.8KW model) and ATC. When they called PCNC tech support about controlling the spindle speed through their Hitachi L100 (provided with the table) they were told that it "can't be done" and "everybody just uses it at 30,000 RPM". I guess when you don't know how to do something it can't be done.

It CAN of course be done and controlled through both the user interface and from g-code with "S" commands. The Hitachi unit has all kinds of ways to control the speed and direction remotely, including the normal 0-10VDC Analog voltage.

I am working with the customer to provide him with better electronics and integrated Spindle Speed controller.

Tom Caudle
www.CandCNC.com

Interesting side note on this particular customer. They ordered their table with an expensive Spindle (HSD German 3.8KW model) and ATC. When they called PCNC tech support about controlling the spindle speed through their Hitachi L100 (provided with the table) they were told that it "can't be done" and "everybody just uses it at 30,000 RPM". I guess when you don't know how to do something it can't be done.

It CAN of course be done and controlled through both the user interface and from g-code with "S" commands. The Hitachi unit has all kinds of ways to control the speed and direction remotely, including the normal 0-10VDC Analog voltage.

I am working with the customer to provide him with better electronics and integrated Spindle Speed controller.

Tom Caudle
www.CandCNC.com


Again: IMHO That's FREE Unlimited Tech Support! Put in a BIGGER fuse!
At least they did not lie: They know they can't figure it out, thus it can't be done.:confused:

If you lose encoder signals for ANY reason you get motor run-away.

That's almost unpardonable when a microcontroller costs less than a buck, it would be so easy to give up if nothing moved when volts were applied :confused:

That's almost unpardonable when a microcontroller costs less than a buck, it would be so easy to give up if nothing moved when volts were applied :confused:

It's not quite as easy as it would appear. Where the motor is at rest it dithers one encoder line back and forth. You have to be able to detect the fact that:

A: you have no step inputs (easy)
B: that the signal from one or both encoders is okay. The problems is that you don't know which encoder channel will dither the most and by how much (set by tuning). With certain extremes of tuning you can get a lapse of a second with no signal followed by a few seconds of one or two channel pulses.
c: Soooo. you have to detect when there is an unbalanced signal greater than the dither freq, (loss of one channel), a total loss of signal on both channels (loss of both channels) but its not in the intermittent dither phase.
d: All of this has to interface back to a power control unit capable of shutting down the power instantly and doing an accelerated load dump (dynamic braking)
e: If we use a >1sec loss of one or both encoder signals as a fault trigger, some of the servo units can travel 5 ft in one second at full speed.



We currently have a "smart" servo interface card in development with an embedded processor but the conditions above make the software a challenge.

We are open to suggestions. Your input for a solution is welcome.

TOM CAUDLE

Hi Tom

If you turn on a motor capable of that kind of speed and get nothing back PDQ you can assume it is either jammed or in communicado. Either way, turning it off quick sounds like a good idea because you will be either blowing fuses or slamming in to things.

A better response might be firing a crowbar circuit, taking out the main fuse at no expense and turning all the motors off :D

best regards

Robin

The motor on a servo unit is not OFF or ON. It's either moving under control of the drive or stationary. The PWM power signal to the coils is always there and the encoder signal controls the position. The failure does not always happen when you turn on the main power.....that would be easier to detect. It often happens when the unit is moving or stationary (rotor locked). The feedback loop in the drive can catch some of the conditions and in our designs a drive fault shuts down everything including power. A crowbar will not only take out the fuse but most likely the drive too since it will be trying to feed current (back EMF) into a dead short. We use a "shunt" approach that uses FETS to place a load across the DC Buss but less than the amount that would damage the drive electronics. There is no definitive signal that can be monitored to instantly detect when a drive is moving without commands from the software. The servo can present a condition on an perfectly good system where there is no encoder output for up to a second If you shut things down for no signal instantly it would false more often than not.

How about an el-cheapo optical wheel with holes (Few bucks?) on the shaft? Two movements on the cheap optical without reasonable feedback from the expensive encoder means you're heading for disaster.

Next level of sophistication is using the el-cheapo to rough calculate your IPM. The el-cheapo could very easily be made within +/-5% of what your precision would be and obviously could used as a trigger for shutdown if mis-matches get great enough.

A 2-LED wheel encoder and wheel would cost what? under $10?

The motor on a servo unit is not OFF or ON. It's either moving under control of the drive or stationary.

Ah! When you said embedded processor I rather assumed you'd put the micro in charge of the chopper disk and the motor windings with something like a National LMD18245.

If you are sticking with your old circuit and the micro is in a supervisory role then you are very safe :D

I must be one of the lucky ones...over a year and it works great!
No problems and when I switched to the plasma the athc worked fine too.
My plasma is what had the problems...


yep it uses geckos and flashcut, I know the stories about PCNC. Ive read joe's blurbs on the internet. I guess i should be just happy that mine works just fine!

I must be one of the lucky ones...over a year and it works great!
No problems and when I switched to the plasma the athc worked fine too.
My plasma is what had the problems...

if you have the pcnc athc with flashcut, trust me, your torch height control does not work great!

I must be one of the lucky ones...over a year and it works great!
No problems and when I switched to the plasma the athc worked fine too.
My plasma is what had the problems...

You are indeed lucky....lucky AND smart, since you are only one of two people I have ever heard say they could make the older version ATHC work at all. Even PCNC admitted to several customers it didn't work. Since you have had your table over a year you have to own the older version. Recently they announced (last few months) that they have a NEW ATHC that is integrated with their control software (WINCNC) that really DOES work. It's only $700.00 more than the old one that didn't.
The really good news for you is that if your unit breaks I know where there are dozens that could be picked up real cheap!:banana:

My PCNC has worked GREAT for a year and a half.
About to go into production for a major chain....
But I have heard of just about ALL machines having problems...
I think its hit or miss either way!
Sometimes a mercedes will break down and the pinto will run forever!
good luck

Gentleman,

I am new here, been lurking for a while. I have been looking at getting a table, 4x8, and will be doing plasma cnc with some routing on the side. I was really impressed with the practical cnc up front, and the price was better, (about 3500 cheaper than a Torchmate 3) but I was a little concerned with their service after the sale, and their reputation. I dont figure 3500 is that much to save if the maching turns out to be worthless. After reading this thread as well as several others, I think it will be the torchmate 3 for sure, as I need something that works not a nightmare. For 18 grand i might have to take a roadtrip and get my money back if I was treated the way people describe on here. Anyways, thanks again guys. Have a good one.
Shane

My PracticalCnc table. runs great...just expanded it .
cutting like a mad man!
Good Luck