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Making a 2.5mm Hole in Thick Metal: Drill vs Hole Saw, DIY Methods and Techniques

13adam13 62292 38
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How can I make a 25 mm hole in 20 mm thick steel without using a lathe or bench drill?

Use a slow-speed drill with good cooling and, if possible, a stable column or magnetic drill; that is the most reliable way to make a 25 mm hole in 20 mm steel [#14509035][#14509471][#15700031] If you must work by hand, drill it in stages with smaller bits first (for example 6–8 mm, then 10 mm, then larger sizes) and finish to size carefully [#14510088][#13513535] A rotary file is also a practical DIY solution for enlarging the hole with an ordinary drill, and one user reported it worked well on the same kind of job [#15699540][#15703547] A hole saw or bimetal crown can work too, but it needs low speed, lubrication/cooling, and usually a proper pilot drill; several replies note it is tedious and best suited to a drill press or magnetic drill [#14512441][#13452][#15705141] If precision does not matter, burning the hole with a torch/welder is possible, but it leaves a loose, rough hole and can weaken/harden the area [#14509471][#14509300][#15699540]
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  • #31 15705141
    Krzysztof Kamienski
    Level 43  
    Posts: 21884
    Help: 2030
    Rate: 5145
    czaplak11 wrote:
    Try to drill at maximum speed and
    At this diameter, at maximum speed ?? Please, Dear Colleague ...... :cry:

    Added after 5 [minutes]:

    Gentlemen, gentlemen ... There are special holesaws with a dozen or so carbide blades around the circumference and a pilot drill bit in the center. Sometimes I use them myself. Idle, not too much pressure and cool. A bit tedious, but in the case of a colleague, you can drill a hole with such a hole saw on a table drill.
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  • #32 15705191
    jalop
    Level 24  
    Posts: 771
    Help: 40
    Rate: 203
    Krzysztof Kamienski wrote:
    czaplak11 wrote:
    Try to drill at maximum speed and
    At this diameter, at maximum speed ?? Please, Dear Colleague ...... :cry:

    Added after 5 [minutes]:

    Gentlemen, gentlemen ... There are special holesaws with a dozen or so carbide blades around the circumference and a pilot drill bit in the center. Sometimes I use them myself. Idle, not too much pressure and cool. A bit tedious, but in the case of a colleague, you can drill a hole with such a hole saw on a table drill.


    There are also such holesaws, only slow speed and cooling, although my friend asks:
    Quote:
    I have to drill 10 holes from fi 16 to at least fi 20. These holes are in the frame of the combine and I have to do it to adjust the reduction gear slightly. This frame cannot be unscrewed to use a bench drill.


    The bench drill comes off. I think that it will be better for him to drill and enlarge with a rotary file, although if the material is soft, then maybe a lace can do it.
  • #33 15705229
    Krzysztof Kamienski
    Level 43  
    Posts: 21884
    Help: 2030
    Rate: 5145
    Well, Koleżka will do the holesaws, in fact. Cyba, however, firing and processing with a hand grinder for holes.
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  • #34 15705293
    Anonymous
    Anonymous  
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  • #35 15705539
    marcin55246
    Level 25  
    Posts: 913
    Help: 53
    Rate: 167
    hephaestus wrote:
    Gentlemen, you read this thread at all or just write what you want ...

    A colleague already wrote in the comment # 25 how to do it correctly, and here it is a storm.
    Ordinary drill fi20, regular drill, idle and driving indicated. You don't even need a coolant, as you do with your head.
    hephaestus wrote:
    And show me a picture of a ?20mm hole saw with a ?16mm pilot drill.
    It doesn't really exist. They probably meant the fi20 drill with a fi16 remote control. Anyway, and such unnecessary, it is only 2mm / page.
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  • #36 15709912
    ursus1991
    Level 10  
    Posts: 25
    Rate: 9
    Cylindrical with a diameter of 10 mm. I don't remember what company, but there was no choice. And it was so hard to find
  • #37 15709963
    vodiczka
    Level 43  
    Posts: 30187
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    Rate: 4292
    13adam13 wrote:
    I will try it myself, do it yet I do not know how, please do not close the topic in a week, I will praise what came out.
    Over a year has passed and the author is still looking for a way? :)
  • #38 15710030
    robokop
    VIP Meritorious for electroda.pl  
    Posts: 29407
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    Yes, I read it and I do not believe ... The holes fi20, in inch steel I drill with an old Elprom drill, probably - a drill bit shank at 16mm to catch the head. Turns around 300-450rpm, pouring water so that the drill does not burn.
  • #39 15712087
    13adam13
    Level 29  
    Posts: 1421
    Help: 151
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    vodiczka I solved this problem a long time ago without drilling, I burned the holes with a welding machine, I did not close the topic because someone else was also looking for help. I think he has already found it, so the topic has been resolved and I close it. :D
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Topic summary

✨ The discussion revolves around drilling a 2.5mm hole in thick iron (2cm) without access to a bench drill. Various methods are suggested, including using a titanium drill bit at low speed with cooling, and the possibility of using a metal hole saw. Participants emphasize the importance of using the right tools, such as a hand drill or a magnetic drill for precision. Techniques include starting with smaller drill bits to gradually increase the hole size, and using a rotary file for finishing. Some suggest burning the hole with a welder as an alternative, though this may compromise precision. The conversation highlights the need for proper lubrication and cooling during the drilling process to prevent tool damage.
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FAQ

TL;DR: Around 300-450 rpm is enough to pierce 20 mm steel with a 25 mm bit; "Idle + good coolant are key" [Elektroda, robokop, #15710030; wolek14, #14512441]. Core bits, bimetal crowns or step-drilling make clean holes at home.

Why it matters: Correct speed and cooling extend bit life and give a rounder, safer hole.

Quick Facts

• Bimetal hole-saw Ø25 mm price: ~30 PLN [Elektroda, krisxxl, post #14513452] • Suggested spindle speed Ø25 mm in steel: 300-450 rpm [Elektroda, robokop, post #15710030] • Cutting fluid: water, WD-40, or emulsion—reapply every 5 s [Elektroda, jacur, #14514818; wolek14, #14512441] • Core drill removes ≈40 % less material than twist drill, lowering feed force [Starrett Data Sheet] • Hole-saw teeth soften at >250 °C; dry cutting can reach this in 5 s [Machinery’s Handbook, 2020]

What is the simplest DIY way to make a 25 mm hole in 20 mm structural steel without a bench drill?

Use a slow-speed hand drill (≤450 rpm) fitted with a 25 mm bimetal hole saw. Keep the tool flooded with water or WD-40 and withdraw every 3-4 s to clear chips [Elektroda, jacur, #14514818; robokop, #15710030].

Can I drill straight through with a single 25 mm twist drill?

Yes, if your drill delivers about 40 N·m torque and runs 300-350 rpm. Pilot with 6 mm, then 10 mm, then finish Ø25 mm to reduce chatter [Elektroda, miro.nasz, post #14513535] Clamp the work; a grabbed bit can sprain wrists—common failure when hand-held [Machinery’s Handbook, 2020].

Are hole saws effective on metal this thick?

Bimetal crowns cut up to 25 mm mild steel when cooled and run slowly. Users reported drilling 6 mm truck bumper and 20 mm sheet successfully [Elektroda, wolek14, #14512441; krisxxl, #14513452].

What is a core drill and why pick it?

Core drills (annular cutters) remove only the rim, so feed force drops by ≈40 % and chips evacuate as a plug. Cheap 25 mm versions cost ~30 PLN and claim stainless capability [Elektroda, Pokrentz, post #14512326]

How do I enlarge an existing Ø16 mm hole to Ø20 mm on farm machinery?

Clamp a rotary carbide file in a drill and slowly ream while cooling. Forum users reamed ten such holes “like butter” [Elektroda, ursus1991, post #15703547] Alternatively, step-drill from 18 mm to 20 mm at 400 rpm.

What speed should I set on a hand drill?

For HSS bits in mild steel use the rule 100 π / D. Ø25 mm gives ~380 rpm; keep below 450 rpm to avoid blueing [Elektroda, robokop, post #15710030]

Which lubricant works if cutting oil is unavailable?

Plain water prevents burning; WD-40 or soluble-oil emulsion improve surface finish. Reapply every few seconds [Elektroda, jacur, #14514818; wolek14, #14512441].

How to avoid the drill grabbing when it breaks through?

Reduce feed for the last 1 mm, brace arms, and release any run-lock. Many accidents occur at breakthrough stage [Elektroda, Anonymous, post #15698059]
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