Thread: using Forstner bits

There are a couple of reasons,

Most tail stocks have a Morse Taper 2 (MT2) so the often used Jacobs chuck has a MT2 arbor to suit. Rarely on wood lathes are they fitted with a draw bar - a threaded rod which threads into the end of the chuck arbor, passes through the tail stock quill and is secured with a washer and nut on the outboard end.

When drilling using any style of bit there is a tendency for the bit to jamb, if the feed rate is to high, if it is not sharp, the wood is green, or the turner does not clear chips regularly. The removed wood "bulks" i.e it occupies a far greater volume as chips than as solid wood, green wood is worse, and if not cleared regularly creates problems. If the bit binds or jambs the force may overcome the friction force between the arbor and inside face of the MT2 recess, permitting the chuck to spin.

Things tend to get ugly if the tail stock is withdrawn while the drill bit & chuck is still in the spinning work piece.

The large diameter of saw tooth or Forstner bits act like a large lever greatly increasing the potential torque force that can be generated. Chips can also build up behind the forstner bit making it difficult to with draw the bit, hence increasing the risk of the MT2 arbor coming loose.

Similar issues occur if a Jacobs Chuck on a MT2 arbor is used to hold work in the head stock. Certain cuts, particularly plunge cuts with a skew, act like a screw thread and will pull the chuck and arbor out of the head stock MT2 recess.

In some situations, rather than holding the chuck by hand I found using the C-spanner (for an ER32 metal working collet chuck) will hold a keyless chuck much more securely and prevent it from spinning in the tailstock morse taper. There are usually several holes in the body of these chucks for the C-spanner hook to hang onto.

They look like this - the C-spanner is the C-shaped spanner in the photo below - the other thing is an ER32 collet chuck usually used on metal turning and milling.
These are precision holding chucks and can be used on WW lathes too.
Screen Shot 2021-03-08 at 5.25.58 pm.jpg

C-Spanners usually come with the collet chucks but can also be purchased separate for about $5.
eg ER32 C-SPANNER #A44 | CTC Tools

Mcjing sell a wrench called an "Adjustable hook wrench" that will fit a variety of keyless chucks but these cost a bit more ~$20
see Adjustable Hook Wrench

The other thing that can happen while using large forester bits on keyless chucks is they can self tighten so much you cannot loosen them by hand. Then, using the C-spanner hanging onto the upper body of the chuck and a rubber strap wrench to turn the bottom part of teh chuck will enable you to loosen the most tightly held bit.
Screen Shot 2021-03-08 at 5.41.47 pm.jpg

Now, I do recommend using the C-spanner with care as a fast spinning lathe may rip it out of your hands and fair smack you on the knuckles. Recommend starting off at slow speed (you should be quite slow anyway using a 2" Forstner) so start off slower still, with the bit unloaded, and gradually apply tail stock pressure and be prepared to let go if it really grabs. Then slowly increase to desired speed. I have never had one hit me in the knuckles but had seen it happen to a turner who was not paying attention. This operation suits a variable speed lathe. If the bit is super grabby it may be safe to use you hands or better still refine you method and/or regrind the bit so it is less grabby.

I usually hold on teh C-spanenr with my left hand and apply the back and forth motion with my right hanging onto the chuck when with drawing.

When metal turning and using large (> 12.5mm) MT twist bits I cannot use a chuck as these bits fit direct into the MT2 tailstock socket. To stop these spinning I have a home made doodad (the one in the middle in the photo below) that consists of a handled attached to a steel ring with M8 threaded holes in the ring. The M8 bolts or socket screws clamps onto the bit itself preventing the bit spinning in the MT socket. This then prevents damage to the bit shank and the lathe tailstock.

Trigrinderhandles.jpg
I have used this bit holder with MT bits on the wood lathe as well but it doesn't really apply to turner's that dn't' have MT shank bits.

very informative, thanks guys.

Dont worry I will treat the lathe and everything around it with utmost respect.

I will also add that most turners forget that the majority of "hobbyist" Jacobs chucks have an arbor with a MT2 one end and a JT6 taper into the chuck body. Even when using a draw bar there is potential for the Jacobs Chuck to come off the JT6 taper.

also, sometimes holding it can stop it from moving wayward once hits center. and secondly the speed at which you are using the lathe when drilling out with Forstner bits is so slow, its rarely an issue.

Originally Posted by Fumbler

also, sometimes holding it can stop it from moving wayward once hits center. and secondly the speed at which you are using the lathe when drilling out with Forstner bits is so slow, its rarely an issue.

Only if the turner is drilling at the recommended low speeds.

How often do you see instructions or a table listing recommended drill speeds for each size Forstner bit included in a set? Never?? I can't ever recall seeing any. Plenty of info online if you know where to look. I've often seen smoke emanating from a Forstner bit being used on a lathe!

Its almost universal that most hobbyists don't have a clue about recommended or ideal drilling speeds for bit type, size & various materials on the lathe or with a drill press. Even if they do most can't be bothered to change belts / speeds on a drill press or 6 speed lathe.

drill2.fh5 (meredith.com)

Originally Posted by Mobyturns

Only if the turner is drilling at the recommended low speeds.

How often do you see instructions or a table listing recommended drill speeds for each size Forstner bit included in a set? Never?? I can't ever recall seeing any. Plenty of info online if you know where to look. I've often see smoke emanating from a Forstner bit being used on a lathe!

Its almost universal that most hobbyists don't have a clue about recommended or ideal drilling speeds for bit type, size & various materials on the lathe or with a drill press. Even if they do most can't be bothered to change belts / speeds on a drill press or 6 speed lathe.

drill2.fh5 (meredith.com)

I agree about the speed issue on drill bits and even more so on hole saws. I've lost count of observing those problems at the men's shed. Not just in wood but in other materials as well.

Just a heads up that most drill speed chart, including the one, above uses a soft European or North American (chart above uses "Rock Maple") as a hardwood reference. This is relatively soft compared to most aussie hardwoods. Rock Maple has Janka hardness of about 6 kN compared to say jarrah which is about 8.5 kN let alone Ironbark which is about 16 kN. This means the speeds for hardwood on that chart should be reduced significantly. For a 2" Forstner in Jarrah I would use about 175 rather than 250RPM. For something like Iron bark it would be closer to 125 rpm. Many DPs or lathes don't even go below 200 rpm which can be a problem which is where a VFD comes in really handy.

There are a number of other recommendations I disagree with on that chart
Onet is that Forstner's are not recommended for use in Al, yet I have been using them in Al for nearly 15 years. The sizes I use are between about 16 and 42 mm. They require a high pressure so DP is essential, a lube is required (I use meths) and a hardwood type speed. The Forstner bits I have been using for this are just the Timbecon budget series and are still sharp enough to drill holes is hardwood. I did buy a quality 20 mm bit when I needed to drill dozens of holes in 1" thick Al a few years ago and that one is also still sharp.
The other disagreement is for countersinks, I use shear cutter countersinks in both Al and mild and stainless steels. I have set of these counter sinks ranging from 6 up to 30mm from Mcjing that I bought about 14 years ago. They are sold as burr removers but they also can be used as countersink bits. Again all at low speed.

Bob, I agree with your comments and recommendations, however the chart is a start and lists all the commonly required info in one chart. The chart recommendations are far better than what you would often see in the Men's Shed.

Originally Posted by Mobyturns

Bob, I agree with your comments and recommendations, however the chart is a start and lists all the commonly required info in one chart. The chart recommendations are far better than what you would often see in the Men's Shed.

Yep definitely agree there.

I have found when using a large Forstner bit when making an insert for clocks is to use a very light feed rate but with the lathe speed not that slow that will tend to hog the bit.

Originally Posted by John Saxton

I have found when using a large Forstner bit when making an insert for clocks is to use a very light feed rate but with the lathe speed not that slow that will tend to hog the bit.

John good point and one I agree with. We are working with wood after all and it does have all sorts of challenges to throw at us, grain, hardness, consistency (open, uniform, early / late growth rings etc), faults, etc. Knowledge and experience with different species, and tasks, plus a basic guide like the chart above, prompt our decision making on "best" drill rpm speed, feed rate, feed force etc even drill bit sharpness. Some woods like gidgee will respond quite well to carbide forstner bits, which are relatively blunt compared to well sharpened high end bits from Colt / Famag etc. but it will be quite the opposite in softer species like pine. No hard and fast rules other than to work safely.

I always tend towards a safety aspect of wood working in my life so agree with your comments.With the lathe especially, wood needs to be of a sound quality only thorough insection of what you mount on a lathe will hold you in good stead.I have known people who with haste had to learn the hard way.With Forstner bits & our really hard timbers being impressed on lathe work I maintain that its best to spend a little more on quality bits rather than going cheap like the ones coming out of the East in recent yrs.