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Forstner Flattening

M

Mark Jundanian

Joined
Jun 6, 2018
Messages
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Location
La Grange, IL
So I came across this huge dry round of walnut at my buddy's yard sale, it was probably about 14 by 6 1/2 in maximum overall dimension. And he only wanted $5 for it, which may have had something to do with it's having a big ol' nail in it. I figured for 5 bucks, I'd take it.

Got it home and was able to excavate and extract the nail with a Dremel, grinding burr and pincers. Now I was faced with how to face off what were very very irregular ends and bring it round to being round, as well.

The first side had the remnants of an oblique chainsaw kerf that left a very large and deep overhanging cliff of wood that was never going to turn off safely, even if it could have been mounted. So my first thought was to saw off the overhang and then plane back the cliff into a slope thinking that with the "gentle" slope I could turn it flat and it would be no more than "jumping a curb". Unfortunately I didn't think to take any pictures until I had finished, but here you can see the large "cliff" that was sawn off and the gentle sloping curb that was left after planing.

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Curb? Yeah, that's going to be more like jumping a Jersey Barricade. Especially since with the imbalance I would only be able to turn this at 300 RPM or so. Time for a plan B.

I cast around a bit for an idea and it came to me to use a large Forstner bit on the drill press with repeated overlapping operations to create a flatter if not actually flat surface.

Here is the block sitting on a plywood skid with shims to level it. The drill press depth stop has been set about a 1/4' above the bottom of the lowest "gully" reflecting that the center pin of the bit is about 1/4" tall.

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The first picture as after the first few runs and the next further in progress.

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Clamps were necessary and the Forstner does not like a lot of overlap and it really has to engage the center pin into the wood first or it doesn't work and play well. Here's a picture of the end result.

SAM_2801.JPG

You can drill off the "stumps" if you can lead with the center pin, but at a certain point it was just easier to use a small flat saw or chisel.

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@Timothy Allen , I have to remember that picture. That could have worked, too. I actually do something similar by putting a square block in a sled then moving that over a router table. There was no easy way to put this irregular piece in a sled, but it didn't occur to me use a traditional router sled, just taller.
 
I have used the drill press often to create a flat surface.

I would judge that irregular surface easy and safe to rough turn as is.
Cuts toward the headstock or tailstock depending on orientation will get that blank in balance in a few seconds on big lathe. A benefit of a ONEWAY 2436 with added outboard Table weight is that it can move an out of balance piece faster than smaller lathes.

If I were using my 20” woodfast i would flatten the blank face since it lacks the weight.
 
Presuming that the blank is securely mounted between centers, or with a faceplate on one side and tailstock live center on the other what is unsafe about truing a blank like that on the lathe? I ask because I true up far more mis-shapen things than that pretty routinely and have never thought of it as being unsafe. I wouldn't do it with the piece mounted in a chuck and no tailstock in place, but between centers what is the danger I should be watching for?
 
Roger Wiegand said:
Presuming that the blank is securely mounted between centers, or with a faceplate on one side and tailstock live center on the other what is unsafe about truing a blank like that on the lathe? I ask because I true up far more mis-shapen things than that pretty routinely and have never thought of it as being unsafe. I wouldn't do it with the piece mounted in a chuck and no tailstock in place, but between centers what is the danger I should be watching for?
Click to expand...

Well I guess it all depends on what someone feels it's safe for them.
 
Roger Wiegand said:
Presuming that the blank is securely mounted between centers, or with a faceplate on one side and tailstock live center on the other what is unsafe about truing a blank like that on the lathe? I ask because I true up far more mis-shapen things than that pretty routinely and have never thought of it as being unsafe. I wouldn't do it with the piece mounted in a chuck and no tailstock in place, but between centers what is the danger I should be watching for?
Click to expand...

It wasn't thinkin' of a general warning of a specific danger, but rather to offer a possible solution in the event that someone else perceived a piece to be unsafe to turn in their hands and shop :). Certainly every one is going to assess a situation differently. I gather, too, from posts in the thread that Timothy referenced that I am not the first person to think of this idea, so I won't claim credit.

Your point is certainly valid, Rodger, but in this instance when I was looking at that lump of wood (to have called it a blank might have been too kind) I did not think it could be securely mounted between centers. Certainly a face plate did not appear to be an option to me and the surfaces seemed too irregular and sloped to securely mount on a star drive. Moreover, the wood was severely unbalanced and I'm gonna guess 15 to 20 pounds overall. Looking at that and knowing my lathe I was sure I would not be able to turn it fast enough for ghost or air gap turning. In my assessment at slow speed there was a high likelihood of a massive catch on the raised area, bad enough to have the potential of dislodging the piece from a sub-optimal mount. As things turned out I elected to leave the bottom in a rough state as I deemed it turn-able. In retrospect I wish I'd hit the bottom with the Forstner, too. As it was the bottom was of differing thickness and unbalanced enough that with the blank rounded and the top already flat-ish I still couldn't spin faster than 350-360 rpm until I got the excess wood off the bottom (and that was more trouble than it was worth to me).
 
Roger Wiegand said:
but between centers what is the danger I should be watching for?
Click to expand...

as I said above safe if you cut Parallel to the bed toward the headstock or tailstock which is what experienced people do. I assume that is what t you would do. So quite safe assuming your lathe is up to it.

What to watch out for:
If you rough trying to cut perpendicular to the ways so that you cut straight into the endgrain the risk is high that you could split off that proud piece and have a flying object.
I see a lot of folks in workshops and classes who try to rough this way.
Awful tearout, rough on the body.
Wood like to be cross cut on the lathe
 
As Mark suggests, the capability of the lathe to handle an unbalanced blank could be a limiting factor. My old Delta 46-700 on a lightweight stand would be hopping all around the shop with the blanks that I trued up in my router jig. My new Sweet 16 probably wouldn't break a sweat truing them up between centers... But I can imagine many chunks of wood out there that would be a challenge still, without some prior preparation.
 
I have frequently used a forstner to make a level landing spot for my faceplate; that makes complete sense to me. I also do it with a big chisel, depending on the situation. Solid contact with the faceplate is certainly important, especially when you are way out of balance.
 
I believe that I would have taken it outside and recut it with the chainsaw. Lots of ways to skin a cat. Sounds like you figured out a way to make it work for you.
 
I keep a small electric chainsaw next to my lathe to trim off any odd shaped pieces on the wood blank when I first mount it on the lathe so it can clear the ways. I also have an angle grinder with a shaping blade for knocking high spots off of odd shaped wood blank that does not clear the ways. No fun getting a large wood blank mounted to a face plate and then mounted onto the lathe spindle and then find out you can't get 360 degree of travel with one or two high spots on the wood blank. A quick slice and dice with an electric powered saw and you can also check the balance of the piece and remove material to get it balanced to run at a higher speed without walking the lathe across the floor.
 
Roger Wiegand said:
Presuming that the blank is securely mounted between centers, or with a faceplate on one side and tailstock live center on the other what is unsafe about truing a blank like that on the lathe? I ask because I true up far more mis-shapen things than that pretty routinely and have never thought of it as being unsafe. I wouldn't do it with the piece mounted in a chuck and no tailstock in place, but between centers what is the danger I should be watching for?
Click to expand...
Darn Roger you beat me to it. I would add that the lathe should be started slow, then up the speed until the lathe starts to vibrate, then back off the speed till the vibration stops. The process of truing the blank may be slow but compared to all the rigmarole required to flatten it first it is still quicker.
A note on the "dry" statement it is highly likely that the center of that piece still holds some moisture that no moisture meter is capable of detecting, so if you are planning to core out several bowls leave them thick enough to twice turn.
 
Glenn Lefley said:
I usually just drill a hole and put on a screw chuck then bring up tail stock. Then flatten one end on lathe.
Click to expand...

Using a screw is a great holding method - disadvantage is the grain orientation is fixed - if you take care in sawing you can get nice grain balance - just keep in mind using a screw center uses the grain pattern produced by the saw cuts.

I’m too lazy to be that precise with the saw
I start most blanks between centers use a spur drive in the center of the planned opening an the tailstock to hold it in place.
Shift the tail center to weight balance. Turn way the out of balance wood some
shift the tail center to balance the grain.
This lets me control the grain balance and alignment.

Some pieces I don’t want to have grain control so I use a screw center.
 
I'm with @hockenbery - I start my bowls (and finish the outside) between centers. I don't ever do it any other way - even if I don't think I will need to fiddle with orientation, it's just easier to stick with one process that works for me.

I use a steb drive center for small things, because I've found that I can tighten it to re-engage if it slips, whereas a spur drive usually keeps slipping once it's dug in.

For larger work (like 5" and over), this is my drive center
IMG_2880-1624344435-1513349391294.jpeg
made from a 3" faceplate and sharpened bolts - the important bit is actually the center point, which keeps the bowl centered. This faceplate had a center hole for a screw chuck.
 
Dave Landers said:
I'm with @hockenbery - I start my bowls (and finish the outside) between centers. I don't ever do it any other way - even if I don't think I will need to fiddle with orientation, it's just easier to stick with one process that works for me.

I use a steb drive center for small things, because I've found that I can tighten it to re-engage if it slips, whereas a spur drive usually keeps slipping once it's dug in.

For larger work (like 5" and over), this is my drive center
View attachment 35202
made from a 3" faceplate and sharpened bolts - the important bit is actually the center point, which keeps the bowl centered. This faceplate had a center hole for a screw chuck.
Click to expand...
Rather unique. We get the point. :D
 
Dave Landers said:
I'm with @hockenbery - I start my bowls (and finish the outside) between centers. I don't ever do it any other way - even if I don't think I will need to fiddle with orientation, it's just easier to stick with one process that works for me.

I use a steb drive center for small things, because I've found that I can tighten it to re-engage if it slips, whereas a spur drive usually keeps slipping once it's dug in.

For larger work (like 5" and over), this is my drive center
View attachment 35202
made from a 3" faceplate and sharpened bolts - the important bit is actually the center point, which keeps the bowl centered. This faceplate had a center hole for a screw chuck.
Click to expand...
Very interesting! A couple of questions:
*How did you sharpen the bolts?
*Can you start natural edge bowls without having to remove the bark?
 
Dave Bunge said:
Very interesting! A couple of questions:
*How did you sharpen the bolts?
*Can you start natural edge bowls without having to remove the bark?
Click to expand...

What I do to mount a NE bowl is to drill a 1 1/4” hole in the center of the future opening.
I then cut the blank to size with a hardboard disc of the size I want pinned to the center point from the Forstner bit with a scratch awl.

then I drive a spur drive into the Forstner bit hole using the point from the scratch awl as center.
By choosing the center first I can plan on having unusual contours or branches in the rim.


I have 3” Forstner bit that could make a mounting point for Dave’s five pointed drive.
 
hockenbery said:
What I do to mount a NE bowl is to drill a 1 1/4” hole in the center of the future opening.
I then cut the blank to size with a hardboard disc of the size I want pinned to the center point from the Forstner bit with a scratch awl.

then I drive a spur drive into the Forstner bit hole using the point from the scratch awl as center.
By choosing the center first I can plan on having unusual contours or branches in the rim.
Click to expand...

I do something very similar for NE bowls. I very deliberately decide where the center of the bowl will be, then drill a 1.5" hole thru the bark into solid wood with a spade bit at that center point. The hole matches the diameter of my spur drive, so the blank is held securely when I mount it between centers. Adjust where the live center hits to balance the blank and reduce vibration at first, then adjust again once the blank is round to get the rim orientation I want.

Process works great. The only drawback is that it's a real hassle to change where the spur drive hits the blank if I discover I chose poorly where to drill the hole. That's why I'm interested in @Dave Landers sharpened bolt drive, curious to hear if it works when pressed directly on the bark, without the need to drill holes or chisel away bark. Seems like his drive could make it much more convenient to adjust the position of the blank on the drive end.
 
Al Stirt uses a similar drive, but it only has 3 pins (a center pin and two side pins), so that you can pivot the workpiece on the drive (adjusting the location of your live center) to easily balance the grain -- see http://alstirt.com/PDF files/NewBowlDriver1.pdf

Any large two-prong spur drive could be used in a similar manner (e.g. Al compared his BowlDriver to a Oneway Big Bite).
 
Dave Bunge said:
Very interesting! A couple of questions:
*How did you sharpen the bolts?
*Can you start natural edge bowls without having to remove the bark?
Click to expand...
I sharpened the bolts once, the first time, by chucking them in a drill and going to my old grinder (i.e. not the good wheels I use for sharpening). That was probably 6 or 7 years ago, haven't touched them since. They're still pointy enough to do the job.

I do often start NE bowls without messing with the bark. The bolts are pointy enough to get in there and hold, usually. They are threaded into the faceplate with a locking nut, so I can also adjust a couple of them longer if there's too much curvature or irregularity on the log.
If the piece has thick bark, I usually chip off some with a chisel or small hatchet.

Timothy Allen said:
Al Stirt uses a similar drive, but it only has 3 pins (a center pin and two side pins), so that you can pivot the workpiece on the drive (adjusting the location of your live center) to easily balance the grain -- see http://alstirt.com/PDF files/NewBowlDriver1.pdf

Any large two-prong spur drive could be used in a similar manner (e.g. Al compared his BowlDriver to a Oneway Big Bite).
Click to expand...

I can see that 3 might be a better number in a lot of cases. Mine has 4 pins because that's where the holes were in the faceplate I used.

Although if I mount the NE side of a log with some curvature, I can orient the 4 pins so that they all hit at about the same length. With 3, one will be too short or too long. So the count of pins probably doesn't matter that much in the long run.
 
My method for this situation is the way Roger Wiegand approaches it. Depending on the size and shape, I first find the best place on the piece to use a 3" Forstner bit to flatten the surface for my faceplate and bring up the tailstock live center and true the blank. I would never turn a piece like that with out tailstock support. :eek:
 
Timothy Allen said:
Al Stirt uses a similar drive, but it only has 3 pins (a center pin and two side pins), so that you can pivot the workpiece on the drive (adjusting the location of your live center) to easily balance the grain -- see http://alstirt.com/PDF files/NewBowlDriver1.pdf

Any large two-prong spur drive could be used in a similar manner (e.g. Al compared his BowlDriver to a Oneway Big Bite).
Click to expand...
This is similar to Brian McEvoy's (Canada) Elio drive. His business was bought by Tod Raines of Woodturning Tool Store (Texas) and the Elio drives are now only available in two sizes - but can now be used with a drawbar (optional) which isn't needed unless you want to use it as a MT2 faceplate.
The socket head pointed screws are a PITA to adjust with an allen wrench when necessary. I always wanted to find a hex head socket to fit my 1/4" ratchet wrench to simplify the process....but I always forget to do that until I go to use it. :(
https://woodturningtoolstore.com/product-category/lathe-accessories/
 
When cutting a bowl blank from the log take the time to use the tip of the chainsaw bar to cut through the bark for either a live or drive center.

IMG_3256.JPG

I'm a big fan of the Oneway Big Bite but for some reason they don't make it to fit a Vicmarc chuck. I made my own for both the 100 and 120 Vicmarc's. Never use anything else.

IMG_3263.JPG
 
Roger Wiegand said:
Presuming that the blank is securely mounted between centers, or with a faceplate on one side and tailstock live center on the other what is unsafe about truing a blank like that on the lathe? I ask because I true up far more mis-shapen things than that pretty routinely and have never thought of it as being unsafe. I wouldn't do it with the piece mounted in a chuck and no tailstock in place, but between centers what is the danger I should be watching for?
Click to expand...
I was going to say the same thing Roger. it would probably take less than 20 seconds to true up that blank on my Stubby 1000. I can see that can be a problem on a small lathe.
 
I have used a forstner bit and the drill press with the depth stop set, many times to level out a spot for the face plate, and even on natural edge pieces. A 3 inch face plate will leave room for several cores. I have found that with careful lay out of your blank before you mount it, grain orientation, in the bottom of the bowl can be done prior to mounting, rather than mounting and moving it a couple of times. I generally don't worry about that though. Of course, some times there are pieces that you never can get centered for the ideal grain orientation because it is one way on one end of the blank and a totally different way on the other end.

For Mark's piece, I would have drilled a flat for a face plate and gone from there. Probably a bit faster to level it up on the lathe. I still prefer a drilled recess and expand into that. Haven't used a face plate in years.

robo hippy
 
I would have just used a 1 3/4" forstner bit to make a flat spot on ea side, and mounted it between centers with a 1 1/2" spur drive, and a Oneway or Robust pointed live center on the other. On pieces with bark, just go down deeper with the forstner. Trying to rough flatten some of those pieces first, before turning, could be more dangerous than just using your lathe for what it was designed for. The only time I will ever work on a piece before mounting it on a lathe, would be to peel loose bark off, or pop off pieces with crack in them, where I am afraid that it would catch and fly off when turning. Sometimes with a deep ridge in the middle, you just need to wack a chunk out with a wood chisel first before using a forestner bit.
 
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