Accurate positioning of sawtooth bit.

[ernie1]

Good morning Charley, As a newcomer to the UK workshop I am hoping there will be an answer to my simple query. I am looking for advice as to very accurately drill blind holes in turned discs using my pillar drill. I have marked, with a bradawl, where these holes should be but find it difficult to accurately set the sawtooth but exactly over that point. Is there some aid which will allow me to sight the bit so there holes are spot on? Any advice would be most welcome. Ernie1

 

[Dibs-h]

Good morning Charley,

Sorry, Charlie "don't live here anymore." vaguely sounds like a song I heard years ago. :lol:

On a serious note - http://www.axminster.co.uk/colt-maxicut ... rod847314/

have a regular drill bit that forms the "pilot" bit and should be adjustable - allen key on the side.

Dibs

 

[ernie1]

Many thanks Dibs for your suggestion and link. The item you suggested is a very expensive piece of kit for my purpose. I'll have to think of something else. Nevertheless I'm grateful to you. Ernie1

 

[Dibs-h]

Ernie

How big a hole are you drilling? Could you not use a spade bit? Somewhat easier to locate.

Dibs

 

[Hudson Carpentry]

Welcome.

Sawteeth bits have a bit of a point in the centre. You just lower the drill enough to see the point of the drill bit sit into the hole made by the bradawl. If its not quite on the hole you keep tweaking the location of the piece until the point meets the hole. Once there mated you plunge for the cut.

If you wish to only sight up on disc as your doing many then get some scrap sheet material, nail/screw a fence down two edges so there 90deg to each other, making a "jig". Bolt or clamp the jig to the drills table and adjust the jig until the bit drill where you want it and tighten up. Then its simply just placing the disc on the jig knowing (as the fences are 90deg or ish) it will always locate in the correct place for the hole.

 

[Steve Maskery]

Can I suggest that you pop the position with a centre punch rather than use a bradawl, it's more precise. Then use a twin-lip-and-spur bit (if the size is suitable, of course).
Steve

 

[ernie1]

Dear HC and Steve, Very many thanks for your replies to my posting. I will follow up your words of wisdom and trust my efforts are successful. Regards, Ernie1

 

[kirkpoore1]

This is an application where a drill press laser really helps. Once set up, you know where the center on even a large bit is going to land. I routinely use one with a 3" rosette cutter (with no central point) and a 3-1/2" sawtooth bit. I can focus on clamping the work at exactly the right spot without dropping the bit to the work to verify where I'm going to drill.

Kirk

 

[ernie1]

Dear Kirk, many thanks for your reply. I have seen reference to the laser aid for the drill press but have not seen them advertised in the UK. Sounds a great help. Regards Ernie1

 

[Benchwayze]

Hi Ernie,

Welcome to the Forum...

If you turned these discs, wouldn't it be more accurate to drill, using the tail-stock chuck of your lathe?

Alternatively, start the hole with a flat-bit of the same diameter, then line up your sawtooth, fix the workpiece, and away you go.

When using a flat-bit, I usually switch off the drill, and let it run down before withdrawing, as flat bits tend to 'rag' the edges, which means a clean-up afterwards.

However, once you have made the 'L' shaped jig, already described, that is the least fiddly and cheapest option. But for the cleanest hole, I would turn to the router, a straight cutter, and the 'L' jig. To position your router exactly, you might need a centre-point , but those are inexpensive, and useful for any number of jobs.

HTH