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Thread: Drilling holes
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23rd Nov 2009, 06:38 PM #1
Drilling holes
Forgive my ignorance but I'm trying to improve my metal working skills. I need to drill holes in 4130 metal sheet (1.5 - 3.5mm thick) and I'm not sure of the best way to do it to get an accurate hole and not overheat anything. I have access to a large drill press but will probably have to buy drill bits. The holes vary from 8mm-22mm is dia.
Should I step drill the parts, working my way up to the required dimension?
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23rd Nov 2009, 10:53 PM #2Most Valued Member
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The use of a Step Drill would probably be the best way to go.
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24th Nov 2009, 04:46 AM #3Novice
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I'm no expert on this but I have had some success in drilling metal sheets and cast iron on a couple of projects. I set the speed on my drill press in accordance with the equipment's guidelines and used cutting oil throughout the process.
For thicker metal, I backed the drill bit out occasionally, clearing the filings and adding more cutting oil. I also made sure I wasn't pulling down too hard on the drill press lever.
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24th Nov 2009, 06:38 AM #4
4130 Is a chrome-moly grade .I am curious as to what the application is.?
All I can think of is aircraft application.
It drills and taps reasonably well.
If using it for an aircraft application there are rules to follow,but I suppose you would know that already.
If using a step drill on a drill press,I would put the sheet on a ply backing sheet and dunnage to raise it off your drill table as your stepdrill may get damaged by contact with the drillpress table.
The drill press method is preferable over a hand held drill as it will offer better control.
Grahame
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24th Nov 2009, 11:16 PM #5Golden Member
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With such thin material I suspect you may have problems getting reasonable holes in the larger sizes if you are using a conventional twist drill, even with step drilling. I think that even with step drilling the drill will tend to catch in the workpiece as it breaks through and leave a ragged or three lobed hole because there is not enough thickness of metal to guide the drill, particularly in the 1.5 mm material. For the bigger hole sizes my preference would be to use a rotary cutter such as a hole saw or, possibly, a rotabroach, which is more controllable in thin metal.
For the big holes another alternative might be chassis punches such as:
https://www.alltools.com.au/shop/ind...is_Punchs_QMAX
I have not used these, but see that they are rated for 1.6 mm steel, so would probably handle 1.5 mm 4140 - I don't know this though.
Frank
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25th Nov 2009, 08:38 PM #6
Yes - it's for an aircraft. I'm building a replica of a WWI design, the Nieuport 17. It was a classic design and very capable for its time:
Nieuport 17 - Wikipedia, the free encyclopedia
The rules for building an "Amateur built - Experimental" aircraft in Australia are surprisingly lax. I will have periodic inspections by a LAME but in the end I need to satisfy myself that it's safe to fly.
The original design calls for mild-steel for brackets and fittings. I'm using 4130 as it is the defacto steel to use in aircraft but no one can tell me why! The rest of the airframe will be as accurate to the original as possible (or my wallet can afford!).
Thanks for the replies - I'm trying to make this as good a quality build as I can.
franco - I might look at hole saws for the larger holes - will be a bit safer too. I have access to a large drill press with some good clamping options at least.
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25th Nov 2009, 10:08 PM #7
The issues are the depth of the step drill.
When a large diameter is to be drilled the point end extends well through the sheet.
To avoid damage to it the procedure is to clamp it to a thick bit of sacrificial ply with some 3 x 2 noggins under the ply to raise off the table.
In school we did projects with the kids with sheet down to .4mm and got a great finish.
1.5mm - 60 thou no worries , but I am uncertain on thickness to 3.5mm thick I would go with a holesaw there.
Folding it may present a problem as the higher tensile strength may require a stronger folder than what will suit mild steel.
Grahame
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25th Nov 2009, 11:36 PM #8Most Valued Member
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Hougen Rotacut sheet metal Hole Cutters.
http://www.google.com.au/url?sa=t&so...51QVl6zdYL5ydw
Simpson Welding Products : Wollongong : Welding : Engineering : CNC : Thermal Oxygen Gas Cutting
Nev
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26th Nov 2009, 12:15 PM #9Senior Member
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Why not correctly ground flat bottom drills With the centre (web area already ground) just entering (and locating) the cutting edges will cut a nice circular hole with the addition of cutting oil.
No good making a mountain out of a mole hill!!
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29th Nov 2009, 03:33 PM #10Why not correctly ground flat bottom drills With the centre (web area already ground) just entering (and locating) the cutting edges will cut a nice circular hole with the addition of cutting oil.
No good making a mountain out of a mole hill!!
I agree, time tested method. Take your time and use plenty of cutting fluid and the drill points will last and its far cheaper.
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