Laser cutting info for modellers

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Busted Bricks
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Laser cutting info for modellers

Post by Busted Bricks » Wed May 01, 2019 8:17 pm

It seems a few members took mild offence when I brought up the topic of laser cutting in another thread. I don't want to hijack that thread so thought I would start a separate thread where we can talk lasers and set the record straight.

There is some outdated information about the cost and capabilities of laser cutting floating around on this and other forums. However things in the laser industry have moved fast in recent years and things have changed a lot.

Those of you that are 16mm members may have read the articles by Malcolm High in recent issues of 16mm Today and very good they are too. Well worth reading.

In this post I will give some information about steel/metal cutting lasers. If there is interest I'd be happy to write about lasers for wood/plastics. I own both types.

Technology:
The gizmo that produces the laser beam is called the source (or resonator). Not that many years ago nearly all sheet metal cutting lasers used CO2 sources. These require a constant flow of gas through the source and are not very energy efficient. The beam is directed to the cutting head via mirrors so they require a fair bit of maintenance. Watt for watt, they are not as fast as fiber lasers due to the wavelength of the laser light - it is not as readily absorbed by steel as the wavelength of light from a fiber source. Although there are still many CO2 lasers in operation around the world, sales are down a lot and most companies buy fiber lasers now.

A fiber laser is a solid state device that uses special diodes to produce the laser light and it transmits the light to the cutting head through an optical fiber cable. It's quite efficient - up to 25% conversion rate (4kW in - 1kW output). It doesn't require any regular maintenance and has an expected lifespan of 100,000 hours. There is not optical path to align/clean. Prices are coming down all the time. Just the past year prices on IPG sources (US/German manufacturer) have dropped twice. There are a couple of Chinese manufacturers now that offer fiber sources at very competitive prices.

Mechanically a laser is not all that complicated. Linear rails with rack and pinion drive, servo motors. The cutting head must be able to withstand the pressure of the assist gas (more about that later) and is water cooled to keep the lens from being damaged. It has automatic height adjustment (capacitance measurement) so it keeps a constant focus distance to the metal.

Capabilities:
Steel is cut using oxygen as assist gas. It create an exothermic reaction, effectively boosting the performance of the laser. However it can create problems with burn-through if the distance between cuts is less than the thickness of the material. If this is an issue, nitrogen can be used instead but that then halves the cutting ability. Stainless steel is normally cut using nitrogen under very high pressure as assist gas. The gas blows away the molten metal and prevents oxidation of the cut edge (important if you have to weld it aftewards). Brass, copper and aluminium is also cut with nitrogen. Brass, copper and alu all produce a highly reflective melt bubble during piercing of the metal. This reflects back into the laser source and can damage it. On older CO2 lasers these materials could not be cut. They can be cut on fibers but require a lot more power than mild and stainless steels. My machine is 1kW and can cut 10mm mild steel, 5mm stainless steel, 2mm alu, 1.5mm brass. It does not have enough power to cut copper.

Machine cost:
If you want to buy a western made machine like an Amada or a Bystronic you won't get any change from several hundred grand. They are commonly in the 3-6kW range but bigger companies are now running 10kW+ machines. However within the last 3-4 years things have really started moving fast in China and they now manufacture a wide range of machines that are very affordable. I have a 1kW fiber laser with a 1300x2500mm cutting area. It set me back £30,000. I know many people that have cars that cost more than that (we have 180% tax on new cars here in Denmark). Low priced machines from China will be a game changer as we have already seen with the small CO2 lasers for wood/plastics.

Running cost:
As already mentioned, fiber laser sources don't require any maintenance. Machine maintenance consists of changing nozzles and protective lens occasionally, lubing the drive components and cleaning off the metal dust and debris. The sawtoothed slat of the cutting bed wear out but new ones can be cut on the machine from 3mm steel so don't cost much to replace. Both CO2 and fiber lasers use assist gas in the cutting process - oxygen for mild steel, nitrogen for stainless steel. Oxygen consumption is not that high and reduces the thicker mild steel you cut. Nitrogen however is used at an alarming rate and the thicker the sheet the more pressure is needed. I can go through a 50 liter bottle (app. 10 cubic meter gas) in little over half an hour. Bought in bulk in 10 or 12 bottle batteries the cost is just under £1 per cbm. I use nitrogen on mild steel below 2mm as it produces better finish and cuts faster.

Cutting files:
Most vector format files can be used. The CAM software on my laser will read DXF and AI format files. However other formats can be converted online or in CAD software. Once imported in the laser CAM software, cutting parameters are set for the given sheet thickness.These are stored so it's just a matter of selecting the appropriate parameter set. Leads ins, lead outs and gaps (if required) are added with the click of a button. Compensation can be added to adjust for the kerf width of the laser beam. Takes less time than it took be to write this. If a customer is not able to provide a vector format drawing then I offer a drawing service. Simple shapes like a model loco side frame can be quickly drawn in CAD based on a sketch with dimensions. I and most others charge based on time consumed.

Material cost:
Steel is app. £1 per kg, stainless about £3 per kg. A 16mm loco chassis probably weighs under 1kg even for a large loco. Haven't checked the cost of brass recently.These prices are for buying in bulk. If you want to buy a small piece of sheet cut to size from the metal merchants the cost can be considerably higher.

Setup cost:
Most large scale outfits have a setup charge - here they range from £40-100 and it's applied per sheet thickness. Others have a minimum order amount. This is to cover the cost of placing the sheet on the machine, changing nozzle, adjusting gas pressure, focus etc. I have low overhead so I only charge £11.50 in setup cost. If customers who only want a few small items are willing to wait I will sometimes waive that charge. Then I can add the parts to a job where I already have the appropriate sheet on the machine. I also waive the setup charge on orders above £115.

Quotes:
I calculate quotes based on material consumption and cutting time. The CAM software will calculate a fairly accurate cutting time. I have set rates for oxygen assisted cutting and nitrogen assisted cutting. Lasers are fast! Even my small 1kW machine will cut through 1.5mm steel in the blink of an eye. I estimate side and buffer frames for most 16mm scale locos could be cut in less than a minute. My hourly rate is low by industry standards but so is my overhead. The machine itself was not that expensive, I don't have people employed to operate the machine, we live on an old farm out in the sticks that cost less than a garage in London.

My conclusion is that laser cutting as a resource for modellers is very much an (affordable) option. Even though a few one-off items will have a high-ish price due to setup costs, just 2-3 sets of parts will lower the cost per part considerably. If you ask around on this or other forums or Facebook groups, there might be people who would also be interested in a set of parts. They might also be willing to help with the CAD part. UK based Model Engineers Laser already has cut files for a number of published designs. If you enjoy marking, drilling, sawing, milling and filing your own chassis parts that's fine - stick to that. However laser cutting can be a viable alternative that doesn't require a second mortgage. That's my take on it anyway - feel free to disagree or ignore my ramblings :)

Michael

PS: To give you an idea of the cutting speed, here I'm cutting a gear from 3mm stainless steel:
https://youtu.be/cJm32zJreLk
Last edited by Busted Bricks on Wed May 01, 2019 8:22 pm, edited 1 time in total.

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Re: Laser cutting info for modellers

Post by tom_tom_go » Wed May 01, 2019 8:21 pm

Thanks for taking the time to put this together.

Moving to the help and advice section and making it a sticky.

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Re: Laser cutting info for modellers

Post by Busted Bricks » Mon Jun 10, 2019 12:10 pm

Here are some loco chassis parts I recently cut for a UK modeller. 2mm mild steel. Total cost of £14 excluding postage.
locoparts1 small.jpg

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Re: Laser cutting info for modellers

Post by tom_tom_go » Mon Jun 10, 2019 12:31 pm

How much was postage?

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Re: Laser cutting info for modellers

Post by philipy » Mon Jun 10, 2019 12:33 pm

Thanks Michael, that is really helpful and informative.

I assume that the £14 you mention is simply the material and cutting cost? i.e No drawing/set up cost - you said it excluded postage, of course.

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Re: Laser cutting info for modellers

Post by Busted Bricks » Mon Jun 10, 2019 3:15 pm

Tracked shipping was £16. It just sneaked past 1kg. For just a few quid more I could have shipped 20kg!

£14 was for cutting and material. I normally charge £12 for setup cost per sheet thickness but this was a special offer for the locobuilders Yahoo group members, where I would waive the setup charge provided they could wait for the parts until I had a larger job for the laser using the required sheet thickness.

Customer provided a dxf file so there was little for me to do on that front.

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Re: Laser cutting info for modellers

Post by Busted Bricks » Mon Jun 10, 2019 3:26 pm

Cost is always going to be on the high side for one-of job. I'm cutting skips for a customer today and as he has ordered 10 sets, the cost per set works out very reasonable. Postage is also a tricky one. The bands are 0-1kg, 1-5kg, 5-10kg and 10-20kg. Each band only goes up by a couple of quid.

I have recently changed day job and I now operate a tube laser cutter, so basically I operate lasers day and night, 7 days a week :D

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Re: Laser cutting info for modellers

Post by idlemarvel » Mon Jun 10, 2019 6:25 pm

Very interesting even though I am not a metalworker. Please could you do a similar write-up for plastic/wood cutting? Thanks.
Dave Miller
currently building the 5" gauge Circle Line

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Re: Laser cutting info for modellers

Post by Andrew » Tue Jun 11, 2019 3:05 pm

Very interesting...

My project to laser cut some NWNGR 4 wheel carriages has stalled for so long that I've forgotten everything I learned, so I might be in touch when I've got a little more time and money...

All the best,

Andrew.

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Re: Laser cutting info for modellers

Post by RobRossington » Sat Jul 06, 2019 1:15 pm

This is all very interesting. I’m looking to scratch build myself a tender engine in 16mm scale. I was intending to use a proprietary chassis, but that example chassis you’ve posted looks much better.

What would be the best format for submitting a design for cutting?

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Re: Laser cutting info for modellers

Post by Busted Bricks » Sat Jul 06, 2019 1:57 pm

The best is a file in dxf format. However I may be able to convert other formats. If you don't have CAD skills I can create files from a dimensioned drawing but it is work that I charge for (£36 per hour started plus VAT).

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Re: Laser cutting info for modellers

Post by jim@NAL » Wed Aug 07, 2019 9:37 pm

Very interesting thank you

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