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Good afternoon
I want to drill several 19mm dog holes through mdf consisting of 3 board layers that is about 60mm thick in total. I don’t think a spade drill bit is up to it.
What would your choice be out of a) twist drill bit ($52 from Bunnings), b) forstner bit, c) auger bit or d) some other style drill that isn’t super expensive such as a router spiral cutter.
Thank you.
John
An auger bit would give the straightest holes, a forstner bit would give the cleanest.
Are you using a drill freehand? If so then an auger bit. If you are holding the drill in a plunging jig then forstner is the go.
And welcome to the forum!
For MDF either,
CMT Forstner Bit - 19mm - TCT | Carbatec
or
If you can find any in Australia, a Colt Maxicut Forstner
Plus one for forstner bit...
Buy the best quality you can afford as they will repay you for years.
JohnQuote:
Originally Posted by Johnwilson
I'm going to ask the WHY / FOR WHAT PURPOSE question.
You mention that you are using 3 layers of MDF -- which implies a bench top.
And you want to drill 19mm dia dog holes.
Do these dog holes need to be spaced accurately? -- i.e. will they be used to ensure that you can use them to accurately cut 90 degree angles, or can they be effectively randomly placed?
How clean does the entry hole need to be ?
Does the hole need to be at 90 degrees to the face of the bench top? -- or can "off vertical" be tolerated?
19mm spade bit is almost certainly the cheapest and AFAIK the easiest to resharpen -- just use a file to re-establish the cutting edge
After a spade bit your options -- in the "isn't super expensive" criteria -- start to get very limited.
Forsteners will make a very clean hole but can wander a bit as they drill down through the wood as they have relatively little vertical guidance but this can be improved by drilling a small (2.5mm) pilot hole and then the trick is how can you drill a straight vertical pilot hole.
You will need a "long" 2.5mm bit - these are about 120mm long
I've used a 60 mm guide block (block with a straight vertical hole) to start the 2.5mm bit hole and made the guide block in a WW lathe. Once the posit hole is started it should hold true.
To make a clean exit with a Forstner, hot glue a piece of MDF at the exit and then remove later.
The other trick is start the hole with a Forstner and use an Auger , and the small pice of hot glued MDF over the exits.
6 of one and half dozen of the other.
Dog holes for a bench top needs to be accurate drilling . It either needs a drilling jig of some sort or a drill press.Quote:
Originally Posted by Johnwilson
Spade bits in a drill press will work . Spade bits free hand drilling wont work.
I wouldn't be free hand drilling for dog holes with any drill bit .
The simplest jig to make for drilling works best with twist drills I think . Pre drill ( on a drill press) a 50mm machined board and clamp over your dog hole position and you have a jig that will start you off in the right direction . Once your in 30mm your well on your way to a reasonably accurate hole.
You cant do the same for Spade bits or Forstner though . As the narrower shank behind the front cutter buggers things up . So its a drill press job or just do your best free hand .
You can get metal drill jigs that guide a drill like a router goes up and down on Rods . Makita type routers . I have one called The drill boy . One of those late night cheap TV add many years ago . They do a reasonable job . 19 mm is large for one of them though .
If you want acurately placed holes make up a base plate for your router that has several 19mm holes acurately drilled for the spacing you want. Plunge a 19mm router bit about 10mm into the top and then finish the hole with a forstner. Use the holes in the base plate and some 19mm dowel to locate your next hole. You can get very good results if you spend a bit of time getting the base plate right.
Good morning
Thank you to all for your replies. About 20 years ago I built a frame for a workbench based on plans for a timber framed bench by welding up SHS and RHS steel pieces. For a bench top I have been using being a single sheet of 18mm chipboard which has worked for my purposes because the frame has sufficient cross members for support.
I want to progress my woodworking. My bench top design calls for 2 sheets of mdf and a masonite sheet cover held in place by cleats using mdf off cuts between the cross members. Twenty years later I’m still fixed on that idea, and now to finish the workbench I bought a Bunnings Irwin 7 inch woodworking vise (which for just under $100 feels sturdy and well made). To accommodate the vise have to cut away a small section of the upper member and weld in a steel plate which I hope to get around doing in the next month or so.
One purpose of the vise will be to clamp wide pieces between dogs in the front jaw of the vise and dogs in the bench top. I have a Carbatec plunging drill guide with a 10mm chuck which I have been practising with a 19mm spade bit on some scrap mdf. The spade bit worked reasonably well up to a point but had some issues such as blunting too quickly, being too slow and sometimes not progressing the hole because the cutting edge was lifting instead of cutting thin layers of mdf and just sliding along the material instead of swarfing the material away. I was practising on a 19mm piece only so I gave up on the idea of using the spade bit for when the day comes to make the bench top.
The Carbatec CMT forstner bit suggested seem like a good idea given that I already have the drill guide. Experimenting with a small 12mm auger bit I had, I think a 19mm auger would do the job very effectively but I would need some practice to control its aggressive cutting action. Pre drilling a machined board for a jig to make a starter hole for a twist drill is another appealing idea - I had success in the past with this idea but only with smaller diameter holes and it worked very well.
What’s important to me is that the holes are straight with minimal tear out out at the top (the masonite cover). I’m not concerned about tear out at the bottom of the hole. Something that requires minimal skill level and is fairly easy to use is also important. Your ideas are very helpful and gives me a lot to work with.
Thank you.
John
I had over 800 16mm holes to drill through 45 thick F27 KD Blackbutt and tried a variety of bits and surprisingly the spade bit was by far the best. The Sutton brand held its edge the longest of the brands i tried
+1 on BobL's 2.5mm pilot hole.
This is the method used in the Parf Guide, which I see on Gumtree with some regularity :)
Attachment 505658
The strange thing was that after the mdf experiment I sharpened the spade bit (a 19mm Irwin from Bunnings) and it worked fine for a number of holes drilled in 19mm Tas oak. I couldn’t repeat that for the mdf.Quote:
Originally Posted by Beardy
John
John
I have a bench similar to yours made from 2 x 25 mm MDF sheets glued together. It has served me reasonably well for about 15 years. I made my dog holes with a Carbatec vertical jig, and used both auger and Forstner bits over the years as I needed new dog holes.
The auger bits made a dog hole that was just slightly larger than the Forstner bits, so some dogs are a bit loose in those holes. For the Forstner bits, I clamped the jig really well to the workbench, and checked the vertical alignment of the jig pretty well before drilling. The Forstner bit I used was just one of Carbatec's standard range, and it cut about 20 holes in the bench before it went slightly blunt. The holes work really well with all dogs.
I found the MDF did make the Forstner bit get pretty hot, and drilled the holes in a couple of passes. It also did not make a clean breakthrough at the bottom, but that was easily fixed with chisel. The entry at the top was clean and sharp. I used a battery drill to drive the jig, and the hardest part was keeping the jig well clamped to the bench so that the weight of the drill did not pull the jig off vertical.
You have most of the same equipment, so I suggest just getting a Forstner bit and doing it.
If you don't need the accuracy of the parf guide, then NCArcher's suggestion of a router and 19mm bit are the way to go. Carbitool make 19mm bits, and Total Tools will be able to get you one.
system workshop: workbench construction part 2 - YouTube
There happens to be a PARF on GT right now! --> $200
The gods favour ye!
It also includes the carbide tipped bit you need :)