Drilling Flat Bottom Holes Query

I am looking for a way of drilling flat bottom holes in timber. I am aware of the various types of forstner and saw tooth drill bits but they all seem to have a center spur or pilot which leaves a hole in the middle of the hole. Using a lathe is not viable an neither is a router. Ideally, a forstner or saw tooth bit without the center spike would do the job it it were available. I have thought of grinding off the center spike but this would leave an area in the center without any cutters. Has anyone any suggestions?

Depending on the size hole and depth but a router using a spiral bit and hole jig works

Buy two spade bits of the size required.
Grind the "spur" and "centre point" off one of the bits.
Using a drill press for safety.
Start the hole with the original spade bit.
Drill down about three quarters of the depth.
Change spade bits and finish off the hole.

This works, this I have done!

Make sure that the second spade bit is in the first hole before switching on the power.

regards,
Ned Black

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Originally Posted by woodbuild

I am looking for a way of drilling flat bottom holes in timber. I am aware of the various types of forstner and saw tooth drill bits but they all seem to have a center spur or pilot which leaves a hole in the middle of the hole. Using a lathe is not viable an neither is a router. Ideally, a forstner or saw tooth bit without the center spike would do the job it it were available. I have thought of grinding off the center spike but this would leave an area in the center without any cutters. Has anyone any suggestions?

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Colt MaxiCut Plus forstners are the solution. Rather than a brad point for centering they have a retractable drill bit. You start the hole with the drill bit very short (or a regular forstner) and then take the drill bit out to complete the hole. Rather than leaving a tiny hole at the bottom it is either flat or with a raised nipple (which can be easily removed). I used them to great effect a couple of days ago when I embedded some REMs in my plane till. The magnets had to be within 2mm of the face of the board to have sufficient strength to hold the planes.

Thanks all for your responses.

As I need to drill various sized holes up to a maximum of 54mm, the spade bit would not really be viable.

The "Colt MaxiCut Plus forstners" sound like they may do the job. However, looking at the Carbatec catalog they only list a set containing 15, 20, 25, 30 & 35mm. Also their description and picture do not show a removable center drill so I would need to check this out further.

I found a site which advertises as follows-

"Series 060 Forstner bits are designed for smooth, round or oval boring, cut a perfectly flat bottom hole, and will bore any part of a circle leaving a true polished surface. These bits can be guided in any direction without regard to the grain of the wood or knots. Unlike others, this style Forstner is guided by its circular rim.
Series 060 Forstner bits do not have a center point."

See http://www.jamestowndistributors.com...53&nobot_crawl

This looks to be ideal for what I want to do. However, the supplier is in the US and I can't find an Australian distributor.

What's preventing the use of a router - maybe we can find a way around that for you

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Originally Posted by woodbuild

The "Colt MaxiCut Plus forstners" sound like they may do the job. However, looking at the Carbatec catalog they only list a set containing 15, 20, 25, 30 & 35mm. Also their description and picture do not show a removable center drill so I would need to check this out further.

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Carbatech only sell Maxicut (with a permanent brad point), not the "Plus" versions, and only in a very limited range of sizes.

I had a good look at the site you linked to. The bits are in imperial sizes and you are quoting metric for your maximum size. Their 2 1/8" bit is 53.975mm according to my conversion tables, which is a suitable equivalent, but it costs US$128 and is special order at the distributors so probably made to order.

You haven't said how many holes you need to drill in each size, the size of the smallest holes, or the total range of sizes needed. However I suspect that a router with template bushes and a small collection of templates would be cheaper and more efficient way to go for a few parts, or alternatively, look at subbing that part of the job to someone with a CNC router. Either way the only real limitation on a reasonably flat surface is that the router bit has to be smaller or equal diameter than the smallest hole.

Thanks again for all the advice/comments.

The reason I had said that use of a router was not a viable option was because some of the flat bottom holes would be in irregularly shaped wood, e.g. branches etc. However, the majority of the work will be in DAR timber.

So I am thinking I will do what I can with a router and for the others, I will either live with the dimple in the center or perhaps fill it.

Alternatively, for the irregular shapes, I could perhaps saw the timber at the depth of the required holes, drill the holes right through the off cut using a forstner bit and then re-glue the two pieces back together.

Either way I am sure I can come up with an acceptable solution.

I used to make containers on the lathe for chop stick and incence sticks. The holes were drilled with a forstner bit and were too deep to clean up the dimple with turning tools. I cut appropriately sized disks from matchingn veneer or thin cork and glued them inton the bottom of the holes and hey presto perfectly flat bottomed holes.

Quote:

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Originally Posted by woodbuild

I am looking for a way of drilling flat bottom holes in timber. I am aware of the various types of forstner and saw tooth drill bits but they all seem to have a center spur or pilot which leaves a hole in the middle of the hole. Using a lathe is not viable an neither is a router. Ideally, a forstner or saw tooth bit without the center spike would do the job it it were available. I have thought of grinding off the center spike but this would leave an area in the center without any cutters. Has anyone any suggestions?

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grind the centre pin off a second forstner or spade bit of the correct size and chuck it in a second drill.
Start the hole with a regular forstner bit and drill till you're within 3mm or so of final depth.
swap drills and finish the hole -- the sides of the initial hole will guide second drill