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Designing for laser cutting in mild steel

Information sought about the best way to position small holes in laser cut mild steel.

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Bob01/06/2018 10:11:07
38 forum posts

What options exist for locating small holes in laser cut mild steel. I am thinking in particular of holes less than the thickness of the material and holes which are to be threaded. I would expect to have to drill the holes to get the size.


Hopper01/06/2018 10:49:42
3651 forum posts
72 photos

Couldn't really say without more detail on the nature of the job, size of parts and holes, accuracy of location and size, etc and the number to be done. It all depends on too many variables. Could range from a rule and centre-punch through drill jig to XY table to DRO on a mill or even CNC.

Edited By Hopper on 01/06/2018 10:51:06

RichardN01/06/2018 11:32:57
106 forum posts
9 photos

You may want to be careful if getting holes precut for threading - I have seen caution advised since the laser cutting can affect the temper of the steel which causes problems when tapping.

Can you get a faint 'engraving' type dot on the surface which can then just be drilled and tapped? or a noticeably undersize hole cut which can be enlarged (removing hard spots) before threading?

I'm not sure of the size of holes you refer to - is this 1.5mm holes in 2mm sheet or 15mm holes in 20mm?


Neil Wyatt01/06/2018 12:14:59
16286 forum posts
681 photos
74 articles

What Richard says, laser cut is very hard along the cut edges, so just get a 'centre dot' for drilling small tapped holes.

Plain holes may as well be laser cut.

Alternatively, get them waterjet cut which doesn't harden the material.

Fowlers Fury01/06/2018 12:16:16
323 forum posts
72 photos

Re 'RicherdN's' posting above ~ all very true...
Laser cutting steel can (will?) affect temper of steel along the cuts.
A tough crust has been formed on ms parts I've had laser cut.
When I've specified a hole position on a CAD drawing, a small cross on its centre has been cut on the returned item.
Usual disclaimer, but why not ask Malcom High of Model Engineers Laser ? I've always found him helpful - if invariably busy !

Also there was a thread here on the topic in 2013:-

Dave Smith 1401/06/2018 13:07:41
74 forum posts
7 photos

High end laser cutting for Aerospace etc uses Argon as the shielding gas. Low end which probably means most of the ME suppliers use CO2 as it is cheaper. Problem is though CO2 change the surface structure and hence the hard skin, You pays your money!


John McNamara01/06/2018 13:38:34
1300 forum posts
113 photos

The old rule of thumb is the hole should not be smaller than the material thickness, As I said the old rule. These days newer machines can make smaller holes than the material thickness. Fiber lasers in particular and the latest CO2 machines. Ask your cutting service what they can achieve.

Tomfilery01/06/2018 20:29:24
111 forum posts
4 photos


It depends on the kit used by your laser cutting people!

I had some wagon axleguards cut in 1.2mm steel with 0.9mm holes centred about 0.75mm from the edge of the job (iirc). The size and position of the holes were pointed out to the company, who had to experiment a little to make it work. They were delighted to find that they could do it (as was I). I subsequently tapped the holes M1.2, though think I probably ran a 0.95mm drill through the holes first, without any breakages, or ill effects. Perhaps I was just lucky!

Regards Tom

Dave Smith 1401/06/2018 20:54:54
74 forum posts
7 photos

To back up John's comments and as I intimated earlier, what you can achieve depends on the the machine available. Just before I retired last Christmas my retirement present from work to myself was a full kit of parts for a Don Young Aspinall. This was all cut on a Trump CNC punch with a laser head using Argon. We managed with a bit of jiggery pockery to laser 1.6 mm diameter holes in 3mm mild steel for the loco and tender side frames. So half material thickness is possible in steel. The thickness to diameter ratio with other materials will depend on how much heat you have to put in. As John says talk to your chosen supplier.


Muzzer01/06/2018 22:13:25
2904 forum posts
448 photos

Water jet doesn't seem to suffer many of these problems. No hard edges, excellent finish etc. Another option for you?


John McNamara02/06/2018 06:34:18
1300 forum posts
113 photos

Water jet works well however it has a few of caveats. The kerf of the cut is a lot wider than a laser particularly on thin materials under 10mm when compared to a laser, it is a little less accurate.

Where water jet comes into its own is cutting stone and ceramics, rubber and other plastics and plastic composites that will burn with a laser, also thicker brasses and aluminum over maybe 10mm depending on the machine, older lasers can only cut steel.

Water jets can also cut steel 50mm thick or when pushed at a cost up to 75mm thick. I have read of 300mm cuts in steel. That may be an old record!

In Melbourne at least where I live water jet is quite a lot more expensive.

Accuracy: Apart from the physical limitations to accuracy, comparing laser cutters to water jet cutters there is the machine programmer and machine operator to consider. Highly accurate cutting requires the machines to be operated at the optimum speed for accuracy, this will be less than the optimum machine speed for production. You should discuss this with the cutting service provider if extreme accuracy is required. It may be an extra charge.

Gases The gas mix used is also driven by cost factors, If you don't want a black edge on steel it can be reduced or eliminated by using more argon in the gas mix. together with slowing the machine down. again at a cost.

On the other hand most cutting services I use quote around +-.1mm maximum error in 5mm steel. There is no point in paying extra if it is not necessary.

To put .1mm into perspective If I make a rectangular hole in 5mm plate say 20.1mm x 5.1mm and make a tennon on the edge of a plate 5mm x 20mm then most of the time I will get a drop in fit. There will be a tiny radius on internal corners. This can be overcome by drawing in small relief areas not necessary for me I just touch them up with a tiny file. To a modern laser 5mm - 12mm plate cuts like butter. As plates get thicker the accuracy reduces slightly.

Normally I will have multiple tenons on an edge fitting into into multiple rectangular holes for bolting or welding Every time I do it I am amazed! They all fit....

When getting a job quoted your job will cost less if you provide a clean DXF file for your part. If your CAD can draw closed polylines use them for all plat outlines and holes. Make sure lines are not elevated above zero if your program can do 3D. If just using lines make sure that every line end touches the next line exactly. Closed polylines make this easier. No line should have a loose end when making a hole.
Before you start ask the cutting service how they want the files presented. If you don't use or have a friend that can use CAD.
Some cutting services will do it from an accurate paper drawing but there will be somewhat a hefty charge.

Edited By John McNamara on 02/06/2018 06:50:49

Ian McVickers02/06/2018 18:54:56
131 forum posts
69 photos

If your cutting thin plate with a co2 laser then you could use a high pressure cutting option with nitrogen as the assist gas. This will give a cooler faster cut and wont harden the edge as much and allow for tapping.

duncan webster02/06/2018 20:12:17
2167 forum posts
27 photos

When cutting mild steel the cheapest option is to use oxygen, the laser heats the metal and the oxygen then makes it burn, generating a lot more heat which means you can cut a lot faster. Sort of high tech gas axe. However you then get an oxide layer on the cut surface which is very rough at microscopic scale and blunts files, cutters etc. To get away from this, and to cut stainless/brass/ally etc they use other gases, typically nitrogen, but then the laser has to melt the metal and the gas blows it away, much slower and more expensive.

You pays your money and you takes your choice. I've only ever used the cheap method, just whizz over any surface you need to machine with an angle grinder, even a Dremel if you're patient.

For thicker stuff where you don't need the high precision, find someone with a CNC plasma cutter. Stuff I've had was cheaper then buying plate and hacksawing it as they nest components to minimise scrap. As always, tell the man if you're not in a hurry, makes it cheaper.

Bob04/06/2018 17:22:25
38 forum posts

Many thanks for all your carefully considered replies. My immediate feeling is to ask for just a "cross hair" mark to be engraved to mark the hole locations. Then centre pop and drill the holes conventionally. As Interchangeability is not an issue in my work I will probably locate matching holes using the first component to locate the holes in the second. Regarding the hole sizes I would want to tap M2 in 3 mm thick plate and really would not want to contend with hard crusty stuff.


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