# Lathe speed for forstner bits



## babylon355 (18 Nov 2010)

Hi, I'm making quite a few yew tea lights for friends and family so bought a Bosch Forstner bit to speed things up a bit. My question is this... Should I run the lathe at quite a fast speed or slower? The bit itself has a smooth outer rim rather than a saw tooth grind so it slices the outer cut rather than saws it making for a cleaner cut.






:?


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## tekno.mage (19 Nov 2010)

The bigger the drill bit, the slower the lathe speed needed. If in doubt start with a slow speed and gradually increase it until you and the drill bit are happy!

You'll find a forstner bit will cut quite quickly into long grain wood, but much more slowly into end grain (as in your yew tea lights). 

Once the bit starts to goes deeper into the wood it will heat up very fast, blunting the bit and potentially heat checking yew. The solution is to keep withdrawing the bit to clear the shavings and allowing it to cool down. If steam comes from the wood you are drilling things are getting rather hot - if you start to smell scotching you've blunted your drill bit!

When I make tea lights (usually from oak) and small boxes (from a variety of woods) I find I can hollow them out quicker with a spindle gouge and scraper than I can drill them out with a forstner bit.

What I've now found as the fastest method of hollowing a hole up to 35mm diameter is using a 3D or MAD drill bit - which is intended to cut in all directions (for plumbers & electricians - it will cut wood, plasterboard, MDF etc) These look a bit like a skeletal version of a forstner bit. They waste end grain wood really fast and clear their own shavings effectively, so they hardly heat up at all - even when used to hollow a 35mm hole 60mm deep into well dry acacia!


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## Bodrighy (19 Nov 2010)

I find it quicker and easier to simply use a spindle gouge on end grain. By the time I had pushed the bit in and out so many times I could have done a few of them. Not a big fan of them anyway as they heat up as mentioned and get bunged up too easily. 

Pete


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## Richard Findley (19 Nov 2010)

Nice work Babylon,

I also agree, slow speeds are best or like Pete said, hollow with a gouge.

In my experience holes upto about 30mm are easy enough to drill but when they get much bigger the forces involved increase hugely.

Give it a try and see. As Kym said, heat checks are a very real danger with Yew so try to stop overheating at all costs!!

Cheers

Richard


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## duncanh (19 Nov 2010)

I'd usually say slow speed.
They're not your standard Forstner, but I was surprised when my Colt cutter turned up and the packaging said to run it at between 750 and 1250 (or perhaps it was 1500). Usually I'd have gone for 500 tops.


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## petercharlesfagg (19 Nov 2010)

I make hundreds of napkin rings and I always use around 500 rpm for the coring. (Not precise because I can never remember the speeds of my old CL3)

Any faster and they expand and start screaming plus the hole gets that little bit larger towards the end, any slower and they tend to bind and not clear of debris.

I would like to find something better because the heat produced, especially in Blackthorn can crack the whole caboodle!

Regards, Peter.


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## jpt (19 Nov 2010)

petercharlesfagg (UK)":24az93uh said:


> I make hundreds of napkin rings and I always use around 500 rpm for the coring. (Not precise because I can never remember the speeds of my old CL3)
> 
> Any faster and they expand and start screaming plus the hole gets that little bit larger towards the end, any slower and they tend to bind and not clear of debris.
> 
> ...



What size do you do the rings at?

Trend 3d bits are very good and avoid a lot of the problems that forstner bits have but they only go up to 32mm.

john


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## petercharlesfagg (20 Nov 2010)

jpt":esg66mqw said:


> What size do you do the rings at?
> 
> Trend 3d bits are very good and avoid a lot of the problems that forstner bits have but they only go up to 32mm.
> 
> john



John, all the centres are bored at 1.1/2" or 38mm (I think), it has been suggested at club level that I try using a flat bit with wings (Now IF (a big if) I could find one I would at least try it out!

Other than that I will have to continue on my wearisome way with the forstner!

Regards, Peter.


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## wizer (20 Nov 2010)

Might it be an idea to use the forstner to do the first 2 or 3mm and then use a spindle gouge? That way you've marked your width perfectly, but can hog out the waste quicker and more pleasantly than with the forstner?

That said a GOOD forstner should be too much trouble. I have a few of the clico ones and when you get over the price, they universes apart from the far eastern rubbish (in branded bosch I shouldn't imagine)


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## babylon355 (20 Nov 2010)

Thanks, looks like I may have been running a bit fast for the first batch but to be fair, the bit went really well. I just used it for speed and consistancy really as I was taking ages with a gouge. It performed well though with a fine, clean cut.


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## duncanh (21 Nov 2010)

petercharlesfagg (UK)":27owm8k7 said:


> jpt":27owm8k7 said:
> 
> 
> > What size do you do the rings at?
> ...



Constable Woodcrafts have some 38mm colt bits. A bit pricey at £33 but I like mine a lot.


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## tekno.mage (21 Nov 2010)

The biggest 3D or MAD bit I've found is this 35mm one http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 2606wt_907

I've tried using large flat bits on the lathe, but the really large ones flex a lot in use and I don't find they cut much faster than a forstner or sawtooth. The 3D bits cut really fast and clean - it's just a shame they don't come in larger sizes.


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