Technique question - drill smooth holes into Knauf board

 
  Gremlin Assistant Commissioner

Looking to drill smooth-sided holes into the board but, every attempt so far using 12mm steel/wood bits gives very ragged edges, more like it is tearing the board.  Any suggestions?

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  davesvline Chief Commissioner

Location: 1983-1998
An 8mm pilot hole first, then a 12mm BLUNT drill bit.

The pilot hole allows a path through, and the blunt edges should avoid the grab/tear effect of the outer edges of the 12mm bit.

Or an 11mm bit and file it out.
Also, drill speed has a big influence. I've IMHO, larger drill bits should be used at slower speeds.

Give it I try I spose?

Regards
  hugh g Beginner

Burn a hole through maybe. Hot wire foam cutter or soldering iron. Make sure it well ventilated though
  Gremlin Assistant Commissioner

Well, I have plenty of blunt drill bits Smile  Will try on some scrap...

Can't use a foam cutter as I need the holes in the middle without cutting anywhere else and....I don't have an old soldering iron to use, only a rather expensive good one that I wouldn't use for things like this Smile
  Neville John Station Master

Location: Sydney
I'm guessing you haven't used these types of drill bits? They leave a nice sharp edge.
  Neville John Station Master

Location: Sydney
Well that picture didn't work! It is a picture of a wood bit called a flat wood bit.
  Gremlin Assistant Commissioner

Didn't try that wood bit as I thought that it may rip the board even more...but I can try on a scrap and report back.

Cheers
  Gremlin Assistant Commissioner

Using flat wood bit:
  • Slow speed to start, rips the "skin" of the board
  • High speed to start, rips the "skin" of the board
  • A medium/slow speed (trial and error) make a cleaner hole, then slightly higher for the remainder.


In any case, start with a 12mm flat wood bit and end up with a somewhat rough 15mm hole...
  roy66 Junior Train Controller

Plunge router with a straight bit.
  hosk1956 Deputy Commissioner

Location: no where near gunzels
Use a 'brad point' or 'spur' drill in a drill press.  Guaranteed great result!
Can be used with a hand drill providing you can drill a true vertical hole.

Wayne
  apw5910 Chief Commissioner

Location: Location: Location.
Use a 'brad point' or 'spur' drill in a drill press.  Guaranteed great result!
Can be used with a hand drill providing you can drill a true vertical hole.

Wayne
hosk1956
So would an auger wood drill bit do it? Seems to need something sharp that will score and cut the outer circle first instead of the centre of the hole. Or maybe a hole saw if you can get one 12mm dia.
  Gremlin Assistant Commissioner

Thanks for all the suggestions, drilling in the middle of a 1.2m*.9m board sort of rules out the drill press Smile  But I will explore other options.
  Oscar Train Controller

You could try metal tubing, brass or aluminium or similar. Twist and punch a hole right through. I saw Ken Patterson do it on foam board to route wires and what not either on his What’s Neat show or more likely the Model Railroad Hobbyist monthly show. I wish I could post the episode link but from memory he may have filed the edge of the tube to sharpen it which makes sense. I’ll search YouTube and provide a link later if I find it but it was just one of those tips I thought to myself at the time, gotta remember that. However, after buying three Knauf boards months ago I’ve gone the pine and cork route Wink
  allan Chief Commissioner

The sharpened tube is a technique used for "drilling" balsa wood, where I imagine that the problems are the same.
  miktrain Deputy Commissioner

Location: Adelaide SA
What about a forstner bit? They are designed to cut smooth sided holes and used in joinery where looks are everything.

Tony
  Gremlin Assistant Commissioner

Re Spade bit:

Tried that early on, I commented on it at the top of the thread...will later play with brass tubing etc. Smile
  Oscar Train Controller

Definitely go the tube route. I looked up Ken's videos the other night, couldn't find exactly what I was after except a couple of small shots of small tubing acting as a temporary conduit as wires were introduced then tube removed. Then I got distracted for an hour watching more shows.

But this morning I thought I'd give the method a try and yeah, problem solved IMO.

I saw a bit of old 1/4" copper tubing in the shed, not exactly round, a bit bent and not squared off.  OD was 12.5mm approx and ID 11mm. I gave it a bit of a twirl on a belt sander to give the tapered sharp edge on the outside. Didn't bother filing the inside of another piece to see what difference there'd be in the foam.

So bit of a twist and plunge into unsupported 30mm thick Knauf board and it worked really well. A bit of tear at first to be honest due to the non squared end, particularly seen below in the incomplete hole. But being less aggressive, but still relatively quick, the last hole at the bottom was smooth as. I noticed a bunch of old tent poles in my shed that would produce a couple of other diameters too. Diameter of the holes in the foam matched the OD of the copper tube. I reckon any thin metal tube will give equally good, quick and accurate results.





Reverse Side.

  Gremlin Assistant Commissioner

Thanks for that, seems to be the way to go Smile
  apw5910 Chief Commissioner

Location: Location: Location.
I reckon any thin metal tube will give equally good, quick and accurate results.
Oscar
Can you still get cork borers?
  allan Chief Commissioner

I reckon any thin metal tube will give equally good, quick and accurate results.
Can you still get cork borers?
apw5910
Yes, but they tend to be too small and not as inexpensive as a bit of tube out of the shed.
  Gremlin Assistant Commissioner

Have played with the router bit for the Dremel and it works perfectly, smooth holes with no ripping or tearing...now to find some longer bits to fit the 3.2mm shank...I need to make holes around 60mm deep...

Thanks for all the help and suggestions Smile

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