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mikejohn
08-29-2006, 01:29 AM
In a recent thread someone mentioned they cut most of their big files whilst sleeping.
This subject has cropped up before.
How many people have there Shopbot running unattended whilst cutting?
Has anyone had problems whilst doing this?

............Mike

gerald_d
08-29-2006, 02:17 AM
A search on unattended gives a lot of comments.

mikejohn
08-29-2006, 03:56 AM
I knew this had been discussed before.
It's a bit embarrasing that it was me that started that thread, and I forgot.


.............Mike

bcammack
08-29-2006, 07:46 AM
Welcome to my world...

dhunt
08-29-2006, 08:08 AM
pictures say more than advice..
7433

dhunt
08-29-2006, 08:12 AM
don't even THINK about leaving your Bot unattended.
this is the kinda thing that happens!
7434

mikejohn
08-29-2006, 08:14 AM
Wow!

dhunt
08-29-2006, 08:15 AM
parting shot..
after losing both X and Y, and well on a crazy path, it then lost Z as well, and finally ground to a halt,
while Operator was out on a delivery run(he left the Bot running)...

7435

dhunt
08-29-2006, 08:21 AM
All that lovely varnish added to the fuel,too..
with lotsa Oxygen provided by the vac.pump.

The 'glowing embers' stage made its way downward into and through the MDF spoilboard,
hit the varnish where I imagine it then burst into true flame,
and then worked its way into the vac.plenum cavities!

You don't wanna know what the inside of the PVC pipe looked like,
and the heat absolutely toasted the pre-filter that cloaks the big main filter in the vac.pump's filter drum.

Took about two days to get it back up and running
Not a pretty sight:
- The Boss was NOT happy!

sawkerf
08-29-2006, 10:11 AM
I had a similar incident. I was drilling holes with a compression bit. The sight of a fire on my brand new Bot was kinda frightening! Kip

elcruisr
08-29-2006, 02:10 PM
Two fires started in five years, both due to hitting metal trash, once in paticle board and the worst one in import ply. That is why there is now a 15 lb CO2 extinguisher hanging by the e-stop. I know some "big iron" guys who keep 5 gallon buckets of water around.

dhunt
08-29-2006, 03:58 PM
5 gallon buckets of water, huh?
that says a lot!
woulda helped to put out this
(top of the spoilboard)
7436

dhunt
08-29-2006, 04:00 PM
- this is what the underside of the spoilboard looked like..

7437

7438

myxpykalix
08-30-2006, 03:10 AM
HMMMM....suddenly i'm hungry for WAFFLES!

bob_lofthouse
08-30-2006, 03:47 AM
We've lost one filter due to the above and during the heat of the summer we were getting smoldering MDF every day.... I'm glad I'm not the only person on fire watch!

mikejohn
08-30-2006, 05:18 AM
Anyone not running a vacuum hold down system had major fire problems?

.............Mike

gerald_d
08-30-2006, 06:18 AM
If you are not running a "sucker", a fire will be quickly detectable by a standard fire sensor. I would happily run the bot unattended if:
- no suckers
- light cuts where the bit won't snap or go blunt
- the file has been proved a couple of times.
If I am still nervous, then add a fire(smoke/heat) sensor. Heck, I have run 10 000 HP engine rooms (with diesel, electrics, freon, lube-oil, compressed air, vent fans, etc) unattended - let's not get so nervous about a little bot. If the risk is fire, put in a fire sensor or two.

If you do run a vacuum sucker, a smoke sensor at the exhaust of the pump should do it.

Anyway, the person who you should really ask about this is your insurance assessor - he will tell you what you need for him to carry the risk. (Same on ships - Lloyds tells you what fire protection you need, and how often you need it checked).

mikejohn
08-30-2006, 09:15 AM
Why do you worry about fire on ships with all that water around?
Now, on Aircraft..........!!!

gerald_d
08-30-2006, 09:26 AM
....disposable

zeykr
08-30-2006, 09:48 AM
I'm installing an alarm system and I thought about a wireless smoke sensor on the bot gantry but understood that the smoke sensors are optical and work by scattering of light by smoke particles and that dust in the air would likely give false alarms. Heat sensor would work, but might be too late by time it triggers. I need to look at what other options there are in smoke sensors. Anyone have a smoke sensor near their bot?

gerald_d
08-30-2006, 10:01 AM
There are ionization as well as optical smoke sensors, maybe even more types.

beacon14
08-30-2006, 07:00 PM
Anyone not running a vacuum hold down system had major fire problems?

Not major but we did get MDF to glow red-orange more than once with our old PR machine - no fire only because we were there to stop it.

Usually it was caused by a small piece of scrap getting sucked partly up by the dust collector and jamming into the dust shoe and/or collet. Ironically, that doesn't happen with the vacuum system as the small parts are much less likely to get sucked away from the table.

dhunt
08-30-2006, 08:40 PM
Most folks use a simple sheet of MDF for a spoilboard,
coz we can't get the fancy hi-tech stuff at triple the price..

MDF comes with a nice smooth factory finish on both of its flat sides.
One of those nice finishes goes straight down against the vac.plenum,
while the top surface quickly gets a large dia. bit skimming that factory surface off.

My thought is that the untouched factory finish on the underside of our spoilboards might act as a bit of a barrier to vacuum flow thru the board,
whereas if that surface/finish were skimmed off too, vac.flow would be better? -or worse?

Does anyone have experience with this?

patricktoomey
08-30-2006, 08:54 PM
David, I surface both sides of my MDF spoilboards. I used to just do the top surface but after I started doing both I did notice an increase in airflow. I get better hold down results by shaving both sides.

beacon14
08-30-2006, 10:03 PM
I thought everyone surfaced both faces

joe
08-31-2006, 08:13 AM
Thanks to everyone who posted photo's of fires. It was a real eye opener.

I'm in the process of designing a new vacuum hold down and will move away from anything wood. I don't cut MDF but use Extira and Trupan and assume they would be just as volitle. Any way, I've had it with the expanding and shrinking wood spoil boards. They need constant attention.

Last week I saw a Gerber Sabre which has some kind of acrylic bed. It felt like PVC. That's the direction I will go.

The use of Shopvacs and wood spoil boards may be as new to the industry as the Shopbot.

patricktoomey
08-31-2006, 09:34 AM
Joe, do you know how they are pulling air through that material? I would be very interested in that as I have had close calls with my trupan spoilboard and am also sick of it swelling and contracting. I am changing my table bed over to a granite base with a Corian plenum board so if I could remove the trupan spoilboard it would be darn near perfect.

gerald_d
08-31-2006, 09:57 AM
Acrylic moves around with temperature and moisture, probably not as much as wood, but us metal guys regard it as "unstable". Also burns quite nicely.

dhunt
08-31-2006, 12:47 PM
I don't know how many of you run air-conditioned Shopbot rooms,
but one of the two Bots on this island lives in an air-conditioned room of its own,
and over the years I think I can attest to the effect such Climate Control has
on spoilboard fluctuations: very little swelling and expansion!
Yeah we're lazy, and we only resurface the spoilboard when it begins to look like King Tut's hieroglyphics, but that's still only 3-4 times a YEAR.
I hear guys in here talking about resurfacing every 2-3 wks. and I think...wow!


Airconning your SB room seems a little extreme,
but at 700 ft. elevation on a small, saline-atmosphere tropical island,
Climate Control of this order is nice to have.
Humidities run high,generally on the island,too
and aircon is nice to have
-both for spoilboard stability(relatively)
and the machine operator.

Does anyone else run an airconditioned Bot Room,
and what is your resurfacing rate like..?

joe
08-31-2006, 02:22 PM
Thanks guys for the info on spoil boards.

Patrick, I've been suspecious about Trupan as a spoil board from the start. I'm now on the search for a good solution. Fortunately we have several forums from which to get help.

Follow the leader might work on products like this so I will look at Thermwood, Techno Isel, etc. I know Gerber has some sort of plastic material, approx 8"X 96" stripes. These strips are perferated with 1/8" holes. Between these ara series of aluminum tracks for hold downs. So you can go either way.

elcruisr
08-31-2006, 03:48 PM
"Does anyone else run an airconditioned Bot Room,
and what is your resurfacing rate like..?"

Shoot, we AC'ed the whole shop! 6000 Sq ft! We build higher end furniture for a niche market and after the first year here we had to do something to stabilize the solid wood and tops before installing them on site. Without the AC we had problems with shrinking resulting in open joints etc. Also, after 20 years of sweating my tail off in southern shops and boat yards it was about time.

We only resurface as a result of the top being cut up enough to start losing vacuum. Another BIG benefit is the spindle runs cooler and that's good news for the bearings. Colombo said that they generaly run 40 degrees or so above ambient but don't like to see no load temps over 145. Well, when the inside of your shop on a hot August day is over 100 then you're pushing it on bearing temps! Now we top out at a balmy mid 80's on the worst day, what a life!

Oh, David, I used to work in St. Thomas, I know all about that carribean heat and humidity! When the trade winds die down, whew! Need any help in Barbados?

bob_lofthouse
08-31-2006, 04:26 PM
The only mdf spoilboard we tend to resurface is a 10 x 5 sheet.

Otherwise we bin 2 sheets of 8 x 4 mdf everyday which do look like "King Tut's hieroglyphics"

We don't skim the new sheets as they don't come with the shiny surface. I've only ever seen the shiny stuff once and we sent it back.

And would you believe on the day I posted on this thread above we nearly lost another filter to the problem.

dhunt
08-31-2006, 04:53 PM
"We only resurface as a result of the top being cut up enough to start losing vacuum."
- I identify strongly with that statement
(thus "King Tut's hieroglyphics")

- re. the offer of help
(the tradewinds have died down, this is the hottest muggiest time of year right now, but no weather systems to make it even worse)..
it's under consideration,believe me:
we may get back to you on that one. Stand by.

joe
08-31-2006, 05:53 PM
I'm not sure why you guys need to replace the spoil board as often as described.

Is this a problem with setting an accurate zero? Does the router fail at the zero setting. Must be the re surfacing process.

There is one unfortunate condition that plagues particle boards, that's stability. For that reason I'm leaving it behind. Re-surfacing seems like a waste of time. I'm looking for a more stable surface material, and one that doesn't catch fire.

I don't believe I've seen a commercial CNC sporting a wood composite spoil board. Then, I haven't been to that many commercial shops. Let me know if there are those who do.

evan
08-31-2006, 07:14 PM
All of the big iron machines that use a Vac-hold down that I've seen (a dozen or so) or used (one) have a Pheneloc Resin material (also seen an aluminum one) that is used for the Vacuum table (the bed with the grid cut into it; typically 1/4" wide grooves). A gasket is placed in the perimeter grooves to make a good seal with the spoil board. A spoil board of 3/4" MDF is placed on top of this. Even if everything is perfectly flat and true you have to cut through the part, hence you will be scaring the spoil board. Even "calibrated" materials (those used in cabinetry and signage) are not perfectly uniform in thickness. By having the bit go a couple of thousandths into the spoil board you don't have to worry about processing (sanding or hand routing) the edges of your parts.
MDF is fairly stable on a day to day basis and it's cheap, hence it's use as a spoil board. As long as the mister in the air is consistant from day to day and you're not loosing suction there is no need to resurface the spoil board. If you loose suction or if humidity has changed you're going to want to resurface the spoil board. If you take of .05" each resurfacing and you keep your spoil board till it 's only a .25" thick that', up to 10 resurfacings.

bob_lofthouse
08-31-2006, 07:15 PM
Hi Joe,

All of the heavy iron machines I've seen who process panels all day long use mdf boards.

We cut so many different shapes on our machine during the day that by the end of it the ply boards being held down start to slip.

Our Hold down is a 15hp fpz.

joe
08-31-2006, 10:39 PM
Thanks guys, Good info.

I visited a wholesale sign manufacturer the other day who was running a 5'X10' biggy iron. They primairly cut aluminum and plex sheets. Which is thin stock and don't rely on any spoil board. I had assumed that was the case for most of the production shops until Evan filled me in.

I have another question about zeroing. Hope I'm not wearing you out. If you zero to the bed and not use a spoil board, wouldn't that eleminate cutting into the bed? What is the advantage of zeroing to the surface top?
When I got my PRT five years ago I started out zeroing to the bed, which worked very well. Can't remember why I switched over.

Also thanks Robert for the Hp info. You must be running a 4X8 unit. My new unit, which is on order, is 5'X10'. I called Seimens Pumps for a vacuum price quote yesterday. You better have a seat.

It was 11k.

Gulp!

mikejohn
09-01-2006, 12:19 AM
Joe
Where to zero cropped up some time ago. I think Bill gave the best answer.
If you want to remove a precise depth of material Z zero from the top. If you want to leave an exact amount of material (or cut right through) Z zero from the spoil board.
Making a 3D (2 1/2D ?) plaque Z zero from the surface. Making 3D slices Z zero from the spoil board.

..................Mike

joe
09-01-2006, 06:53 AM
Mike,

My suggestion to consider zeroing to the base, would eleminate having to replace the sacrifice board very often.

Sure there are reasons top zero , but I feel that's a pracitce used much too often. It becomes necessary to re-zero each time material thickness is changed. It's an easy habit to fall into.

Tabs are probably the most popular way to keep parts from being damaged. By using the bottom zero, and leaving a paper thin amount of the stock, the parts are held fast and can be quickly pushed through.
Just another technique.

mikejohn
09-01-2006, 07:16 AM
Joe
If your cut is going deep enough to touch the sacrifice board, then this is where you really should zero from the board.
If you want a 25mm (1") pocket then you must zero from the top of the material.
Of course, this is not simply a matter of where you Zero when at the Shopbot. You must know where you are going to Zero when you write the file


...........Mike

gerald_d
09-01-2006, 07:48 AM
There is no "right" or "wrong" place to use for zero. We zero from the top surface because the table is seldom visible when a board overlays it.

mikejohn
09-01-2006, 10:27 AM
The problem with zeroing either from the top or the bottom, opposite to my explanation above, means you need to now the precise thickness of the material.

mziegler
09-01-2006, 11:47 AM
If there is a concern about cutting in the spoil board, it possible to z zero twice. First time z zero from the top surface for vcarving and pockets tool paths and then z zero to spoil board surface for the profile cutout tool path.
Also for production runs I like cut into the spoil board to give location there the next part go.
Mark

gerald_d
09-01-2006, 01:04 PM
Another good reason to zero from the top is that all the negative z's in the cut file mean "cutting". Guys doing V-carving will also want to zero from the top.

I don't feel that I am missing anything by always working from the the top. You "bottom-feeders"
might be trying to tell me that I could do less damage to the spoilboard, but I don't spend hours trying to keep the table perfectly flat with air-cons, etc. Just cut a millimeter into the board every-time and dump/skim it when it gets too bad. (A digital caliper quickly tells you how thick the board is and how deep you are going to hit the spoilboard)

Hey, isn't this thread about unattended operation?

joe
09-01-2006, 01:37 PM
Gerald,

I have to go with Mike on this one. Use the technique that best suites the situation.

Many substrates aren't the same thickness from corner to corner. Even 3/4" PVC, can vary more than 1mm. Perhaps that's due to it not laying flat on the router bed. Either way, it seems much better, on profile cuts, to use the final bed height as the standard.

Another reason to zero to the bed has to do with pre-masking the materials. By doing this, and cutting to the thickness of the mask, your parts are held securely in place. Then it's just a quick removal of the mask and the parts fall right out. No bridges or tabs to sand off.

Finally: A vacuum hold down, is much more effecient when the spoil board isn't a fuzz bal. The application of a premask tape also increases the vacuum effeciency while cutting. What I mean by this is, air doesn't escape through the routed area's.

You might even get away with a cheeepiee shopvac.

gerald_d
09-01-2006, 02:05 PM
That's okay Joe, the foodchain would be incomplete without bottom-feeders.


We tend to measure the board thickness at about the same corner (0,0) where we set the z-zero, so the variance in its thickness from corner-to-corner is no more problematic for us than for you.

robert_cheal
09-01-2006, 03:39 PM
I often zero to the table and then VA to the presumed material thickness for my cutting zero.

joe
09-01-2006, 07:22 PM
Robert, That's a proven technique, we also use.

Gerald, When doing a profile cut, you can't rely on a corner measurement as evidence of a panels thickness. But then you aren't a production guy.

gerald_d
09-02-2006, 12:49 AM
Joe, I think we are missing each other here.... When we measure a board thickness at the home corner, and then z-zero at that corner, we have effectively "calibrated" the setup from the bottom of the board, which is the top of the table.
(Not a production guy? - I think 50 sheets a week, same file, counts as production?)

joe
09-02-2006, 07:45 AM
Gerald,
Profile Cuts: If calibration is made at the corner which is too high because the material is thicker, other area's of the panel will not be cut through. Or if corner material is thinner, and a z zero calibration made, you will get cut down into the table surface. All of this is of no consequence by z zeroing to the surface.

mikejohn
09-02-2006, 08:31 AM
If you are profile cutting (cutting right through the material) then the file needs to be made with the precise material thickness known, if you are going to cut with negative Z moves, and zero from the material top.
Otherwise,if the material is thinner than planned you will cut through to the table, which may not be important, if its thicker you will not cut right through.
So by all means measure the thickness of the material, Z-zero on the top surface, but then go off the table, move the Z down the measured thickness of the material and re-zero,(effectively measuring from the table, and have your file with zero at the bottom, positive z moves.
Someone may argue "but what if the table isn't flat?"
In this case it doesn't matter a monkeys what method you use.


................Mike

joe
09-02-2006, 09:22 AM
John,

Let me see if I can explain this one more time.

Many materials aren't the same thickness all the way through, and some sheets don't lay as flat as we would like. Either way, by a botton zero you are home free. Also, if you've pre masked on the down side, and want to cut to this dept, leaving the mask, you'd be hard pressed to do it with a top Zero.

gerald_d
09-02-2006, 10:55 AM
That's okay Joe - your glass is half-full and mine is half-empty - you measure from the bottom and I measure from the top.

mikejohn
09-02-2006, 11:51 AM
7439
If you want an exact depth of cut, like the hole in the red block, zero from the top.
If you want to leave an exact amount, as in the green block, zero from the table.
Assuming even material you get exactly what you want.
The thickness of the material is immaterial.
Finding the table Z by z-zeroing at the top and subtracting the thickness of the material is accurate.
Finding the material top by z-zeroing at the table and adding the thickness of the material is accurate.
I either case, uneven table or material will give problems.

.............Mike

gerald_d
09-02-2006, 12:26 PM
Being after 6pm on a Saturday here, the glass is now less than half-full - Joe says I must use the bottom of the glass, so I have to empty it first. Cheers!

joe
09-02-2006, 01:05 PM
Gerald,

Wish I was there to help empty the glass.
Cheers,

J.

joe
09-02-2006, 01:21 PM
John,

I agree with whole hartedly. Please note, my posts are about through cuts. Profile cuts on letters and parts which cut through the material. The depth of the cut isn't important as long as the part is free at the end. I have often zero'd to a corner, which was slightly thicker or raised which leaves parts attached. The for sure way to cut to the table top, is to zero there.