Chinese (esp Shenhui) bed sizes and safety window

[john banks]

A local seller told me that most 1290 machines don't actually have a 1200x900 bed and are typically 200mm smaller. I think some of you would have noticed and commented, but I thought I'd ask.

Also they said that most machines from China don't come with CO2 laser blocking windows. Any thoughts? Obviously when aligning I'll be very careful and use safety glasses and avoid eyes being anywhere near the axis of the beam too, but it would be a shame if my wife should be wearing them even when the lid is closed, never heard of this before with various Chinese machines resold by local importers used in schools etc.

Sam's laser FAQ http://www.repairfaq.org/sam/laserco2.htm#co2saf says this:

"Acrylic, polycarbonate and glass are all quite opaque to CO2 laser light. However, if plastic is hit with enough of the beam, it will burn through. You might not think this would happen unless you decide to put your window directly in the beam path, but I've seen plenty of windows damaged by the beam reflecting off the work or from fixturing."

I would ask Shenhui, but I'm still bombarding them with questions sorting out the details, the final one I think now is what is the max power RECI I can get into the 1290 with or without an extension to the chassis.

[Michael Hunter]

One or two people on this forum have said that the lids of their lasers have been *marked* by reflections of the laser beam.
You can never rule out anything absolutely, but since any possible reflection is far from the focus point, the power density is low and you would be amazingly unlucky to burn right through the lid.
Plastic lids (polycarbonate, I believe) are the norm - certainly that is what is on my Epilog.

Can't comment on the usable bed size, but this seems unlikely - are you sure that your "local supplier" is not scaremongering in order to get your business himself?

Final thing - if your main interest is engraving, then be careful about having too much power as it might make working with the more sensitive materials difficult : 60 to 80W should be more than sufficient. If it is cutting ability you are after, then of course the more power on hand the better.

[Rich Harman]

My 1,400 x 900 Shenhui has a table that is 1,525 x 972, the cutting area is 1,400 x 900.

The GH690 is still on the boat.

[Rodne Gold]

My 1200 x 800 is 1200 x 800 , I have measured the travel, Lid is as opaque to laser as any other lasers lid is. No glasses required. bombard shenui with as many questions as you want , don't be shy , chinese are very patient and its your money you spending. The issue with high power is that the glass tubes wont fire at under 20% power or so and the machines are slower than the top specced western machines so for engraving that needs very low power and high speed , you might be overpowered.

[Dan Hintz]

are you sure that your "local supplier" is not scaremongering in order to get your business himself?

It's either scaremongering or he doesn't understand CO2 lasers (either of which is likely).

Just about anything transparent you put in front of that laser is going to absorb the beam's radiation. If it hits it long enough to destroy it, you'll know first from the mark being made, and if it's plastic, second from the burning hole. To get to that point, you would have to focus on the same spot on the lid for several seconds at full power. Not very likely.

[john banks]

Thanks all. Scaremongering as I suspected.

We'll stick with 80W RECI (they said 130W RECI is similar size to 80W standard), presently confirming all the invoice details, it is going back and forth quite a lot to get all the details sorted out. A 1290 has changed to a 1280 on the invoice, it has ended up with a load of Rodney's spares for his second machine and the extra motherboard/LCD/stepper driver spares we'll skip, but the price has dropped mysteriously unless something isn't included as the latest invoice doesn't show "RECI" anywhere on it, so the latest invoice is in a Word document with changes tracked and we'll see if that process is smoother. Rodney has kindly offered to review the invoice.

Despite the language barrier, if the price and spec of the standard/base machine was listed (and it seems that it changes so sometimes an upgraded chiller and motorized table are included, and sometimes are charged as extra), and there were option/upgrade prices and spares prices, all listed with a unit price column, quantity and subtotals it would all be much easier, but it is a new experience for us.

Hopefully once the invoice is nailed down that becomes the factory spec/order/basis for packing list etc and it will all work out.

Our shipping company has quoted £520 plus VAT. There is 4.5% duty on (value+freight+insurance), and 20% VAT on (value+duty+freight+insurance+VAF).

The actual freight cost from China to Felixstowe is just a little less than the freight cost from Felixstowe to Scotland!

I love how the UK treasury charge you VAT on the duty, think they do that on petrol too!

I also noticed on Alibaba that they show "die cutter" lasers which have 2x150W RECI and a 1200 * 1800 bed. $17-20k range. Initially our interest was mainly in cutting thicker woods and we revised down our expectations to 4-5mm once we saw how 50-100W lasers cut thicker wood (badly and slowly), we might look at one of these later, or a CNC router with a quiet spindle and soundproofing. I do wonder if the kerf angles on thicker wood would be better with a 300W beam, especially if the focal length can be longer to go with it.

[George M. Perzel]

Hi John;
If you are concerned about open areas on the front and rear of the machine, Shenhui will add removable panels-no charge. I had that done as a precaution as I have grandchildren whose height puts them at risk. Not sure what thickness and type of wood you will be cutting but 80 watt RECI is sufficient for up to 6mm ply and 8mm solid (most woods). Key to cutting wood is a strong air assist flow and modifying the nozzle to have airflow into the chamber under the lens and also at the point of cut. A good exhaust and a supplemental front blower to force air to the back is also desired. Table size is too big for just single exhaust port to handle when cutting wood. You may also wish to order longer focus length lenses- they have them up to 100mm. Make sure you order the honeycomb table-surface is made up of steel core so easy to use magnets as hold downs-needed for thin ply which tends to warp.
Send me your email address and I will send you copy of my Shenhui invoice (dual head, 80 watt, 1280 machine plus spares and a few pics of the airflow mod.
Best Regards,
George
Laserarts
gperzel@rochester.rr.com

[john banks]

Hi George, you have email. Thanks, John

We have made friends with a local factory who make staircases, and they have offcuts of kiln dried hardwoods that are too small for their big machines and ideal for us, and they have been cutting them for us in various thicknesses. Cherry works well, oak often seems to break on the grain when too thin, but they are really good and said they will keep aside the bits that cut nicely for us

[Rodne Gold]

The die cutting laser has 2 nozzles , one cuts from the underside of the wood , the other from the top , meant for dieboards that get steel cutting rule inserted and are used to punch out cartons and the like , the wood moves the nozzles facing each other stay still , I dont think you can cut totally thru the wood with this arrangment , each nozzle would then fire into each other.