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Drill 19mm Work Bench Dog-Holes Experiences - Advice Please

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WandrinAndy

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On a previous bench build, I drilled 108 dog-holes (19mmx62mm) in the MDF worktop of a bench partly based on an MFT (Multi-Function-Table). For holding 19mm Oak dowels, the diameter of these dog-holes is fine, although possibly a tad loose. I first drilled +-25mm with a 3/4" (19.05mm?) Forstner bit, and then drilled through with a 19mm Irwin Spade bit which has since grown legs and run.

However, I recently drilled about 40 dog-holes (19mmx50mm) in another worktop comprised of 18mm MDF and 32mm laminated chipboard, and have a wee problem... the diameter of the holes is a tad too narrow!!! These were drilled through in one go with a 19mm Irwin Power Auger bit.

The dowels are binding in the top MDF layer even before they reach the chipboard.

I am hoping somebody can please suggest an easy way to solve the too narrow dog-holes?

Stupidly I drilled all of the bench dog-holes before checking the resulting holes, as I had recently used the same Power Auger bit to drill 24 holes in 70x70 pine, when making a horizontal timber rack, and the 19mm Oak dowels fitted nice and tight in those holes. With hindsight maybe too tight for bench dog-holes, and I should have drilled the first 5-10mm with the Forstner bit!

Out of interest, a digital calliper measures our current three nominal 19mm bits as follows:

18.95mm = Irwin Power Auger bit, although it is somewhat difficult to measure this type of bit accurately
19.03mm = Forstner 3/4" bit
19.40mm = Spade bit from a cheapish combination bit set

By the way, for the layout I used a sheet of pegboard that was clamped to the worktop while all the dog-hole positions were centre-punched at 4 pegboard holes/inches apart. I used crayon to pre-mark the shiny white side of the pegboard to know where... and more importantly where not... to drill.

Key to me drilling the dog-holes straight was using what I call a drill-through "jig" that I built around a cheap drill-stand-press thingy, that I find works well for this purpose. I am sure others have better ideas for getting the holes straight....

wDSCF2098.JPG


And whereas I felt very much in control with the Forstner bit, and to a lesser extent with the Spade bit, I found that with the Power Auger bit I had to set the drill speed high enough to prevent it stalling, and once it bit (no pun intended) into the work piece, there was virtually no stopping it and the hole was done. I am guessing that this is because of the screw-thread-point?

Thanks,
Andy
 

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bugbear

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WandrinAndy":27s381bm said:
I found that with the Power Auger bit I had to set the drill speed high enough to prevent it stalling, and once it bit (no pun intended) into the work piece, there was virtually no stopping it and the hole was done. I am guessing that this is because of the screw-thread-point?

Thanks,
Andy
I'm always nervous of a screw thread bit in a power tool. Others seem more confident (or perhaps reckless).

BugBear
 

Jacob

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I've only got one dog hole in my bench and it's square.
If your dowels are too tight make them looser. Remember we are woodworkers!
NB you only need a few dowels (2 or 3) you don't need all 1008 or however many it was!
 

AndyT

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I think the thing I would try next would be to use the same drill bit, in the same way, and just work it up and down a few times in a hole. I'm guessing that some of the fibres would have been pushed out of the way, rather than being cut, and are springing back into place. The drill should just be able to wear them down a little.
Nice tidy little jig by the way.
 

Paul Chapman

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bugbear":1i4ykxwa said:
I'm always nervous of a screw thread bit in a power tool.
+1. They are OK in a cordless drill that stops when you take your finger off the trigger but not in corded drills that carry on revolving and being drawn into the wood by the threaded tip.

Cheers :wink:

Paul
 

woodbloke

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Paul Chapman":1070a4oz said:
bugbear":1070a4oz said:
I'm always nervous of a screw thread bit in a power tool.
+1. They are OK in a cordless drill that stops when you take your finger off the trigger but not in corded drills that carry on revolving and being drawn into the wood by the threaded tip.

Cheers :wink:

Paul
Agreed. If you're going to use one of these bits with a thread in a power tool, the best thing to do is to grind the thread away to leave a small point - Rob
 

Paul Chapman

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woodbloke":22ed2f71 said:
Paul Chapman":22ed2f71 said:
bugbear":22ed2f71 said:
I'm always nervous of a screw thread bit in a power tool.
+1. They are OK in a cordless drill that stops when you take your finger off the trigger but not in corded drills that carry on revolving and being drawn into the wood by the threaded tip.

Cheers :wink:

Paul
Agreed. If you're going to use one of these bits with a thread in a power tool, the best thing to do is to grind the thread away to leave a small point
Or just file the thread off, leaving a plain point, as I did with the flat bit on the right in this photo



Cheers :wink:

Paul
 

Harbo

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Yes I had what could have been a nasty accident using one of those with a power drill. I was drilling a hole in some floorboards to thread a cable through - it cut so fast it went through a joist and into a power cable. Enormous bang, melted bit and brown trousers!

Rod
 

Cheshirechappie

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If the dogs are tight in the holes, either 1) sand a bit off the dogs, or 2) wrap a bit of sandpaper round a bit of dowel, and jiggle it in the doghole a bit till a dog fits nicely.

If there a fewer dogs than holes, I might be tempted by method 1.
 

WandrinAndy

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Thanks for the ideas guys.

The dogholes seem ok for hardware such as clamps and holdfasts, as these tend to be a tad narrower than 19mm.

And whilst sanding down a few dowels would work for this bench, I would prefer to get the holes right as I sometimes interchange jigs, that are held in place by dowels, across two different SIL's benches, and the other SIL's holes are correct.

AndyT":a9bk9wgp said:
I think the thing I would try next would be to use the same drill bit, in the same way, and just work it up and down a few times in a hole. I'm guessing that some of the fibres would have been pushed out of the way, rather than being cut, and are springing back into place. The drill should just be able to wear them down a little.
Think you may have hit the nail on the head AndyT and I will try this out when I get back downunder again... sadly only next year.

Thanks,
Andy
 

Steve Maskery

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Bradshaw Joinery":1843kxcp said:
You could try a reamer in the appropriate size?
I think that is a very good idea. Grind a hacksaw blade to 3/4", taper one end a bit.
Turn a wooden peg like a garden dibber, saw down the middle and slide the blade in. You can then ream the holes quickly and accurately. Well, as accurately as chipboard will allow.

Chairmakers use this method to match legs to seats.

S
 
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