Forstner Bits problems

[Deano14]

Hi all i'm a newbie to the wood working world and a newbie to UK Workshop forum.

I have a problem guy's i'm having issues trying to drill/bore holes using various size Forstner bits anything from 15 mm to 4 inches in diameter. I've tried nearly everything to get the Forstner bits to work but i can't see why there not working right for me. I've tried turning the speeds down on my pillar drill to 300 but i'm finding the drill stops spinning and doesn't even cut when i make contact with the wood cause its on a really low speed. so i try to speed the pillar drill up slightly to see if it helps the drill to make a cut with the Forstner bits but they either struggle to make a cut or just catch in the wood again stopping the drill chuck from rotating. I've also made sure that the Forstner bits are still sharp and not blunt. I've tried them on various woods soft and hard but not much luck, i'm loosing a little faith with them now and two of them are quite expensive to buy to not use anymore.

Any help would be greatly appreciated guys thank you

 

[Phil Pascoe]

Once you're over a couple of inches it takes a fair sized motor to drive a forstner, maybe larger than yours. Have you tried the bits in a battery drill or a brace? Does the pillar drill drive large bits of other types? This would give an idea whether your pillar drill is just gutless.

 

[paulm]

Check the belt driving the drill is reasonably tight and not slipping under load, but not so tight as to give problems with the bearings down the line.

After that, it is most likely to do with the power of the motor as mentioned above. At the kind of larger sizes you mention it is likely to be more successful using a router, template and bearing guided router cutter to be honest.

 

[Eric The Viking]

Deano, firstly, welcome!

4" is asking rather a lot as has been said, but... Your pillar drill has a gearbox. As you alter the belts to reduce the speed you are also increasing the torque, in inverse proportion.

Things I would suggest you look at (it's likely to be more than one of these problems:

1. are the bits properly sharp and running true? If there is any wobble they won't work half as well as they should, and the finish will be very poor. They can dull off very fast in man made boards. I bought new Axminster ones for a job in the summer using Buffalo board, and the surface coating meant I had to hone after about six holes.

2. right speed for the bit and the material: bigger needs slower.

3. are you using the right amount of downward pressure? They need to cut - too little pressure and they will scuff, overheat and lose fheir edge. If you get burning this may be a hint. Make sure the depth stop can't slip!

4. are they clean? resin build up adds friction and reduces efficiency, and also causes burning. Can be a problem in MDF and softwoods especially, also some hardwoods like purpleheart (horribly gooey sap).

I think you will struggle with bigger sizes in a small pillar drill. The distance the edge travels goes up with roughly 3x the change in diameter, and the area hogged out with the square of the radius. You might try a holesaw just under the size you want to define the hole but it probably won't help much.

What material are you drilling into?

[edit] Read your original post more carefully. You did say you tried various woods. I think it's probably a combination of insufficient motor power, and bluntness, or that and resin. The good ones (Fisch etc.) are eyewateringly expensive, and I suspect the reason is that they are expensive to make (a lot of machining operations), and doing it all to a high standard ii high quality steel is costly. I have a small set of Colt drills - hugely expensive, but the quality of finish is staggeringly good in comparison to normal twist drills.[/].

 

[MusicMan]

All of the above, but try lubricating with beeswax or even candle wax touch it on while it is rotating.

 

[CHJ]

To help with lack of power on pillar drill try opening up the larger holes in stages.

To maintain correct alignment of the finished hole you need to at least provide a shallow cut with your largest bit to provide final alignment because you will loose the centre support for the bit as soon as you drill deeper.

It will take longer having to change bits but it reduces the cutting torque needed considerably.

Whether you need to stage the various sizes to aid their alignment as you open up depends on how well clamped your workpiece is and robustness of your pillar drill.

Start with your biggest drill. and then take a shallow bite with each smaller one if necessary, drilling to finished depth with the smallest and opening up in stages, the more steps you take the lower the torque needed.

 

[Deano14]

thank you guys for your help will definitely try all you have suggested thank you again :deer :deer :deer

 

[Bodgers]

Even on my cheap small Rexon drill press I can get through hardwood with a 15mm Forster, so I'd say you have dull bits. Cheap, dull bits are even worse.



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[oakmitre]

I have a cheap TimberTech pillar drill. It is basically the same as all the other cheap pillar drills out there.

I you look at the first two photos in the following link on Amazon https://www.amazon.co.uk/Timbertech-Spe ... B00D840RHQ

You can see that on the left side of the drill there is a hinge, and on the right side there is a black tightening knob. The belt is tightened by pushing back on the motor housing and then tightening the knob.

Until I bolted the drill down, It was difficult to get enough tension on the belt and tighten the knob at the same time without the drill threatening to fall over. It seemed to be tight, but the belt would slip.

 

[CHJ]

Use a large flat bladed screwdriver or a wooden wedge in the gap between drill mounting and motor mounting plate and apply appropriate belt tension whilst doing up the clamping bolt/s.

 

[Bodgers]

If you are at the point where you are resorting to belt tension then I'd say you need to look at the sharpness of the bits.


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[profchris]

I've used a 1.5 inch Forstner in a hand brace, and it takes a fair bit of down pressure to make it cut and a lot of grunt to swing the brace. But at hand brace speeds it shifts quite a lot of wood in each rotation. Sharpening makes a huge difference. Not sure I could hand swing a 4 inch bit though!

If you have a hand brace you might try drilling a test hole or two to get an idea of the amount of down force required to start the cutting. I found that it took a lot of down force to get it started, but much less to carry on from there. If your drill is a bit underpowered, it might even be worth trying to start the holes with a hand brace, and the continuing with the pillar drill.

 

[GLFaria]

re. the belt slipping, if you are using standard v-belts in your DP, you might want to shift to toothed v-belts of the same size. They can be used with the common v-pulleys used on most small DPs.

With toothed belts I manage up to 35mm Forstner bits in softwood with my tiny 250W DP, provided the bit is freshly sharpened, that I go it carefully, and that I take the bit out every 2-3mm depth or so for cooling.

I found out waxing the bit may or may not help - still not sure.

Another source of trouble, as far as I'm concerned, is the central point of the bit - that piramidal shape is not vey good at cutting, and in some bits they are huge. I got the habit of previously drilling a small diameter hole - say, just large enough that the point goes in about half its length - to ease this problema. I don't know if this is a good practice, but it's the way I manage with the larger bits.

With a couple exceptions, I use Bosch Forstner bits. Not the best, but expensive enough for my budget.