Information sought about the best way to position small holes in laser cut mild steel.
|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.
3588 forum posts
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
|106 forum posts|
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 Wyatt||01/06/2018 12:14:59|
15947 forum posts
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 Fury||01/06/2018 12:16:16|
319 forum posts
Re 'RicherdN's' posting above ~ all very true...
|Dave Smith 14||01/06/2018 13:07:41|
|66 forum posts|
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 McNamara||01/06/2018 13:38:34|
1288 forum posts
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.
|108 forum posts|
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!
|Dave Smith 14||01/06/2018 20:54:54|
|66 forum posts|
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.
2904 forum posts
Water jet doesn't seem to suffer many of these problems. No hard edges, excellent finish etc. Another option for you?
|John McNamara||02/06/2018 06:34:18|
1288 forum posts
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.
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.
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.
Edited By John McNamara on 02/06/2018 06:50:49
|Ian McVickers||02/06/2018 18:54:56|
|114 forum posts|
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 webster||02/06/2018 20:12:17|
2067 forum posts
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.
|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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