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Bill Price
Unregistered
| | Posted on Saturday, December 10, 2005 - 08:33 pm: | 
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Background:
The following are changes done and planned to the shopbot I bought in Sept 2005
I am retired and as such can probably spend more time tinkering
My background is electrical, I have a son who is very qualified in computers and an associate who is very qualified in various mechanical processes and materials
The Bot is a PRT 48, would have preferred a 96 but shop is small
As a lot of the changes are simple and quite invisible, I am supplying this documentation
The changes are for:
- Safety
- Production
- Ease of use
Spoil board
The table is ¾” mdf over ¾” ply
The ply is mounded with recesses carriage bolts
The MDF is mounted with a good number of grooved wood dowels driven in a slightly smaller hole
This will make changing the board easier, simply drive out the dowels, put new board on top, drill new holes from below and drive in more dowels
Hold down
My research on the web and review of the forum indicated no one method would work for all projects and some were quite expensive!
Tried screws but were time consuming and damaged the spoil board
But will probably use them once and a while for special occasions
Built and installed a edge clamp that runs on rails attached to the legs on the Y sides
It is driven by a garage door opener and controlled by a heavy duty joy stick
This allows me to load and clamp / unclamp in seconds!
The next version will use tongue and groove hardware flooring for the edges with a simple and quick replaceable edge made from another piece of flooring
I have also used it successfully on 1” high-density house insulation foam with out a problem of buckling
This stuff is approx 1$ a square foot versus 11$ for the sign foam. Not as good in a number of respects but ok for cheap signs
Limitations are in using thin materials that will buckle when edge forces are applied
For large sheets of thin material, I have the plans and parts for air-activated clamps along the x-axis. It should allow me to do a number of thin sheets, at the same time
{Grounding and electrical noise (EMI)}
The number of comments on the forum regarding grounding is quite significant and often talked about as if it was quite mystical
Since the bot operates in a system using both high drive and low signal voltages, heavy and noise current drawing devices and in an environment prone to static, proper grounding is a must
My ground system uses the industrial method of a common ground point at the nearest hydro ground point.
(The separate hydro ground was verified that it went back to the main panel and lightning rod ground)
Then a common ground connection was created at the point where two separate hydro fused plugs were installed for the bot and its computer. From this point I ran separate heavy #14 leads to the:
- bot frame.
- The router case ( I do not trust the set screw or grounding through all the mechanical connections)
- The controller case (had a problem with grounding to case at back, seemed to be a coating on the metal, and it really had to be tight to get through?)
Reducing static electricity. So far I have had NONE
The nature of the cutting creates static electricity, so it is here to stay
Running a ground wire around or in the vacuum system will obviously help and is usually the basic practice.
I have part of the vacuum pipe grounded at the bot at the frame as it comes with a ground clip and the rest grounded back to the dust system along with other machines it shares. All the rest of the equipment is grounded in a star fashion back to the common hydro ground
All ground wire for all machines whether separate or part of a 3 prong system are at least #14 wire or bigger. I have kept the power runs to minimum lengths with minimum connections
The computer and controller are plugged into power strips with surge and noise protection
The computer station which is covered in clear plastic to keep the dust out has heavy aluminum tape along the front grounded back to the common ground loop on the back to ensure the operator does not discharge into the key board or mouse when coming from the work areas
Over the years I have found the best thing to fight static was to keep the humidity in the shop at approx 50%. If you check it is also the best for your health
EMI
The router draws large amounts of current through brushes and as such is very noisy electrically. To reduce the EMI from this I added two snap on ferrite cores over the electrical cord right where it comes out of the router case. These are very simple to put on and cost me 1$ each at the surplus store
Comments on various bot forum discussions on grounding
Generally speaking:
- if you get a little snap when touching or approaching the bot, it is more likely static. It can happen if you are charged and the bot is grounded or if the bot is charged (NOT GROUNDED) and you are grounded.
Obviously we would prefer that the bot is grounded. One thing I don’t know is what will happen if you create a spark to one of the controller inputs, like the zero plate or the limit switches. If not designed right, it will eventually destroy them
- If you get a continuous tingle or more, then you have a hydro leak, which is very dangerous for many reasons. I would also suspect this happens more often standing on a cement or conductive floor. In this situation turn everything off and fix it or get some one who can!
A number of bots use the frame ground at a leg or rail for the zero plate. Unfortunately due to bearings and a very good coat of powder paint, getting a reliable path through to the computer is only luck
The Zero plate signal level voltage is 5 volts and only a few micro amps, which is not enough to punch through paint or oil or dirt. This is no problem for static or the hydro voltage, but I would not take a chance
In industry, as a matter of safety and operation reliability, they would have a flexible cable to all moving parts and special lock washers to break through the paint and ensure rigid parts are electrical connected
Limit switches
Limit switches work fine but can move / swing a little on the little connector bolts
People handling the machine can inadvertently move these with out realizing it. Thus changing 0,0 reference
To prevent this I added loc tight to each one
Computer control of the router and dust collector
Bought the relay option from shopbot that allows you to control a relay from the computer
Shopbot mounted it inside the controller case so as to connect it to the control board
It has a single contact relay that will control 15 amps
I didn’t want to bring a noisy router power supply cable into the cabinet and I wanted to control at least two different power sources, one for the router and one for the dust collector. This will probably be expanded to control yet another circuit for vacuum hold downs and other accessories
To do this I used a multi-contact slave relay mounted outside at the ground point. One set of contacts runs the router and the other the dust collector, thus keeping a lot of EMI outside the controller box!
Now one thing I never trust is having a piece of computer controlled equipment that I have to work on.
So I created a simple lock out switch using the router bit changing wrenches
The wrenches are mounted in spring clips at the end of the table where we told the bot to go after a cut. This is not the 0,0 position but a point much easier to get at for changing bits
When the operator pulls the wrenches, one wrench switch drops a relay back at the control point interrupting the power to the router relay. This means that no software or computer glitch can inadvertently start the router during a bit change operation The other wrench switch operates a lock up relay that sounds a beeper and activates a led to remind operator to re zero using the zero plate
To use the relay circuit from the bot software, my son wrote a little program that sits on the computer desktop. To use it you simply drag your cutting file over top. It brings up a window asking what options, currently just the relay and the bit change position
Once option is selected, the program will return a modified file to the original directory leaving the original one intact
The program automatically inserts the relay code at the beginning and end of the file as well as the new final position for ease of bit changing. Only takes seconds!
When you say start, the router and dust collector start up, cutting is done, router and air go off and machine moves to bit change position
This or equivalent should also help in reducing router on time and thus bearing life.
It should go a long way to helping shopbot sell the relays!
Cable management
This is important because you don’t want a cable to come lose or damaged / broken in a middle of a cut!
A bar was put across the back of the controller box and all incoming / outgoing cables were tied to it to act as a strain relief so as to keep the cables from being pulled out of the controller
A bungee cord connects the stand (on wheels) that holds the computer and controller to the wall so that the operator can’t strain the cables
All cables to the bot are in protective flex pipes to reduce wear and such from operators and equipment
Heat and the computer
We put the computer a laptop in a semi closed mobile station to protect it from dust
To keep it cool and acting up during a cut we added a fan with a thermostat to keep it cool
Zero plate and all
Proper grounding is a must for using the zero plate
When we got the bot we had a problem with Zero plate grounding, which turned out to be the ground connection in the handle of the little clip they give you to attach to the bit or collet. As long as there was tension you had ground but when lose no ground.. This resulted in the bot trying to drive the big v bit right through the Zero plate breaking the tip off. That is when I ran a separate ground right to the router case
This also eliminated the need to try and hook up the ground clip under the skirt, a difficult and dangerous (if forgotten) activity
To make it easy to position the ground plate, I added two leds to the dust skirt along the x-axis and the bit. Now I can just put the plate under, verify the led lights are on the plate and hit enter.
Quick and easy!
The zero plate comes with a short piece of aluminum channel with a sticky back so as to hold the plate when not in use. This was useless. I threw the plate out and put a piece of industrial Velcro on the plate and the y carriage and it is now very secure and easy to use. * Pictures
Speeds and feeds and the amp meter
Speeds and feeds versus bits and materials seem to be quite mystical in this business. As I have no experience, I searched the web, suppliers and such and got a lot of suggestions, but what really works with out damaging bits and materials
So I hooked up an AC ammeter to the router and monitored the current used for various combinations of bits, speeds, and materials. If the router was groaning I check the current draw and vary the feed and speed to reduce it. If the router appears to be having a free ride I can increase the feed and speed to something less then the current draw that will cause groaning
Dust collection
Have added an extra blast gate near the machine and a vacuum gauge to that I can vary the vacuum for special cuts like foam.
The gauge allows me to repeatedly set up the right level
The dust skirt connection to the short piece of hose that is supplied by shopbot needs to be tapped. A fair amount of leakage occurs at this point.
Shop safety
The following items are used to ensure a safe working environment.
If you have other workers or visitors in the shop you will need to consider the following as you are quite probably liable if some one is injured or has to work in unsafe environment
- Noise level, had a professional audiologist verify the need for sound protection and have enough muffs for all
- Put in power vented a fume hood for painting
- Power failure exit lighting
- Fire extinguisher
- Extra dust filtering
- Humidity monitor
Future plans
Micro switches on the drive motors to stop bot if something jams and motors move to jump gears
Disable bot from moving when operator is changing bits
Simple release clip on dust collector skirt
Add a hour meter to track how long router runs to manage bearing change outs
Heat sensors on dust skirt to monitor overheating or fire
What has not worked!
Remote keyboard made from a game controller, tried this but not reliable. As near as we can tell the software can’t handle high rates of keystrokes, Probably a software buffer over flow problem. It was very handy when working
Regards Bill |
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