Robo Hippie - Question on dovetail tool

[John K Jordan]

...Threaded? Threaded for what? Do you mound directly to the headstock spindle?

I thought he meant use a screw chuck with a waste block but hard to guess. I have never done that - if I glue on a waste block I mount it and the block between centers, turn it round and use it for a tenon, end or side grain.

Maybe a sketch would make things clear.

JKJ

[robert baccus]

Roger that John--the word after threading is single screw as in single screw chuck. I have turned hundreds of bowls/vases with tough hard glue blocks CA glued to the piece. The block can be single screwed on, chucked on with a screw on ring 0r tenoned in to a chuck(yuk) or whatever. When attaching he glueblock to the bottom of the piece try the following. The glueing can be clamped between the tailstock point and the drive point for perfect alignment. Turn the lathe on and mark the high point with a pencil if this helps align the joint with a rubber hammer. You have a few minutes with thick CA to adjust the joint if necessary. My absolute favorite on heavy pieces is a screw on ring(dovetailed,-by Nova and others)(I have many shop made and factory) With thick CA glue on a #2 Nova chuck with #2 jaws. It holds 100#+ long vases on fresh green wood. Screws hold poorly in endgrain and are almost useless in weak, green endgrain sweetgum. This combo has held many without fail--I love vases and urns and they have leverage yeah. Enough smoke? The dovetail being useless was my error--I forgot people use 3 and 4" dovetail holes. I use 2" jaws for everything and it is impossible on my yellow thing to make a 2" dovetail between centers because of the tailstock interference--they do work very well where there is room . Enough words!

[John K Jordan]

...The dovetail being useless was my error--I forgot people use 3 and 4" dovetail holes. I use 2" jaws for everything and it is impossible on my yellow thing to make a 2" dovetail between centers because of the tailstock interference--they do work very well where there is room .

For soft wood like walnut, sweetgum, etc. I almost never cut a dovetail on the inside of a recess even when using dovetailed jaws - I find the wood deforms nicely and makes it's own dovetail to conform to the chuck. For osage orange, black locust, many exotics, yes I make the dovetail.

For 2" recesses a scraper ground like this can make a dovetail easily. (This is not in use for this recess, just showing the scraper on a recess made on the drillpress.) This one is ground from Thompson scraper stock.

scraper_recess_IMG_20170911_140404_923.jpg

I often grind scrapers for special things and then regrind for other things on a whim.

JKJ

[Reed Gray]

Hmm. This gets a raised eyebrows from me. I never cared for the screw chucks. It surprises me that they would give enough of a grip for a solid hold, even in a hard wood. Considering that it works for you means I may have to rethink this... It would seem more reasonable to me if you had a hardwood block that matched the threads on your headstock spindle though. For sure, you need a dead flat surface. I don't like glue joints, unless I have to have them. I know they work, but I don't trust them.... Yes, I am stubborn....

The only situation where I will never use a recess is when I am turning end grain. Having a 4 to 6 inch tenon with jaws to match, and with a dove tail would work, well at least I think it would. I don't like the idea of crushing the fiber to get the jaws to seat firmly as this would create uneven stresses from top to bottom. Probably not a big deal if you are roughing, but I haven't experimented with it.

I do know that Lyle Jamieson uses lag bolts for his bigger end grain pieces, and I believe they have big coarse threads. For sure driving nails or screws into end grain is not a good grip. Any old timer carpenter knows that you always toe nail (drive at an angle) when going into end grain because it holds so much better.

robo hippy

[John K Jordan]

Hmm. This gets a raised eyebrows from me. I never cared for the screw chucks. It surprises me that they would give enough of a grip for a solid hold, even in a hard wood. Considering that it works for you means I may have to rethink this...

Reed, I find the screw chucks hold very well. (but I don't use them on end grain!) That said, I almost always turn dry wood. For bowls and most platters I use the old Glaser screw chuck on the top side first, cut a recess or tenon and outside, then turn around to hollow. (I do like the Glaser screw better than the wormwood screw that comes with some chucks)

This has always felt secure even with relatively large pieces. (I don't think I would use it on a heavy, unbalanced chunk though!) I've never had a piece come off even when turning squarish platters at pretty high speed. (no catches, of course!)

I've turned platters to nearly 20 inches with the screw chuck. To turn the outside and base, following Frank Penta's instructions, this was chucked turned with a central screw as well as turned three times off-axis, all with a screw chuck:

platter_PC012780_e_comp_small.jpg

I've used screw chucks in dry sapele, walnut, cherry, maple, and even soft eastern red cedar.

JKJ

[robert baccus]

I use screw chucks on heavy pieces with a tailstock support for sure while turning the outside of vases. The inside gets hollowed and the whole piece gets finished after cutting off the wax and outside rough wood while on thr screw. It took me several years to work up to this procedure very carefully! I like to find the edges in performance--an old racing habit perhaps. Boats, cars, atvs sailboats ect. Like John the glaser makes the best screw but the 5/8" nova never fails--in dogwood, beech and tropical hardwoods. Hence the glue connection--hard screwblock/glueblock to any wet or dry turning wood. Wood unlike metal can be difficult to faster even if a good structural material and required all the help it can get. Good and fresh CA is rated at 5-6000 psi--do the math on a 3-31/2" glueblock.

[John K Jordan]

...Good and fresh CA is rated at 5-6000 psi--do the math on a 3-31/2" glueblock.

I have never once tried CA to hold a glue block, just Titebond and only on dry wood. A glue block sure would save on expensive exotic woods and I already have several drawers full of ends of blanks a little too short to hold in the chuck. (all dry wood) I might try this for the small pieces but would probably hold the square waste blocks in the chuck jaws.

Do you sand flat first on a disk sander?
Favorite brand of CA?
Does it hurt the joint if the clamping pressure is too tight? (more squeeze out)
Let cure by itself or use an accelerator? (I understand accelerator may make the joint more brittle)

Ever try this on cocobolo and other rosewoods or ebony? Any time I use CA on cocobolo I have to work very quickly since something in the wood acts like an accelerator. I haven't tried CA on ebony but it would be nice if it worked. I guess there is no harm in trying since a 2" cube flying off the lathe is not the same issue as a 100# chunk!!!

JKJ

[robert baccus]

John, after researching glues and trying all the types over the years I find --Titebonds and others hold on dry wood only and with clamped joints only--CA required neither. You can put CA on a GB and just set it on a turning piece--just a small weight to keep it level. Working on wet wood with no screws means no waste wood as in nice or purchased wood. Miracle stuff! Chucking up with a SS or a metal dovetail ring type screwed to apermanent glueblock lets you change a piece on or off in seconds. This allows me to rotate 5-6 pieces while finishing--wetsanding the lacquer on one--swapping to another for shooting a coat of lacquer ect. Allows me to do various procedures with two spray guns and what ever nonstop. I'm Really bad to allow finishing to stack up on me--this goes very fast allowing several to dry on the rack while working on another already dry. I seldom glue on greasy hardwoods but they are very dry--probably work yeah. I do worked down lacquer finishes always requiring several steps--very fast and glasslike finishes. Days faster than WO poly ect. I was never crazy about any poly finish--looks too plasticy. You can grab your lac. wet vase by grabbing the GB with a big channel lock pliars and letting the lathe back off the SS threads while you hold the pliars with both hands transfereing the piece to the shelf to dry. Screw on another and keep working. John, I flatten GB's on the lathe and premake several ahead in several sizes ready to go with Rings screwed on and holes predrilled and prescrewed on the SS to thread them. Lazy huh?

[Brice Rogers]

I made a dove tail tool. It uses a piece of high carbon steel as an insert and is attached to a square 1/2" bar. I sharpened it to 80 degrees. On dry wood it works great. I can position the cutter so that I can put in a recess without the tailstock getting in the way. So, it is like John's purpose ground scraper.

But recently I was putting a recess on some mulberry. It was a sick tree and its moisture content was not all that high. The problem I had was that the wet wood wouldn't give me the typical whispy shavings - - probably because it was semi-green. So I applied more pressure and then I got something like a mild catch. It really dug in. I'm not sure what I'm doing wrong. I'm wondering if there is too much cutting surface. The cutting surface is roughly 0.6". Anyone have any experience here?

Today, I took one of the inserts and reduced its cutting area to perhaps 0.35 inches. I'm hoping the this gives me better control. I haven't tried it yet as I still need to reharden it. For inserts, I don't bother to anneal them. I prefer them to be "dead hard" and haven't had any break on me. But I'm also careful not to drop my tools on the concrete.

[Leo Van Der Loo]

Brice some years ago I needed to make a recess while the tailstock was in my way to use my regular used tool, so I used a cheap carbon steel scraper tool and ground it so it sits on an angle on the toolrest, it has just a pointy end and I can push it in and make a nice sharp corner, I use it only occasionally but it’s handy to have.

recess tool.jpg

[John K Jordan]

...So I applied more pressure and then I got something like a mild catch. It really dug in. I'm not sure what I'm doing wrong. I'm wondering if there is too much cutting surface. The cutting surface is roughly 0.6". Anyone have any experience here?...

Do you have a photo of the tool? Understanding the geometry of how the bit is orientated with the shaft and the toolrest support may suggest the problem and solution. Most catches are due to a lack of support, the reason for the shape and grind on the scraper I showed, to provide as much support on the tool rest as possible and put the cutting edge in line with the support to help prevent force from the wood from twisting the tool. I made that one on a whim but if I used it often enough I would probably regrind it with a different shape to allow the tool shaft to be more perpendicular to the toolrest to make it even easier to use.

[Brice Rogers]

John, Here is a picture of the tool. I use it to clean up a partially made recess and to give me the dovetail undercut. If the tailstock is not being used, I usually orient the cutter to be in line with the shaft and just plunge it in and apply pressure to the left to cut the dovetail recess. If the tailstock is in the way, then I orient the cutter insert 90 degrees (like a flag). In that case I essentially pull it (towards me) into the partially made recess. To deal with the rotational forces, I use an outrigger stabilizer on the shaft (that is, I snap on a vice grip). I also try to minimize overhang on the tool rest. On dry wood and freshly sharpened it works like a dream cutting (actually scraping) very cleanly and give fine whispy shavings. But recently on the damp mulberry it didn't. It was grabby and hard to control.
IMG_0021 (1024x768).jpgIMG_0020 (1024x768).jpgIMG_0017 (1024x768).jpg

[John K Jordan]

John, Here is a picture of the tool. ...On dry wood and freshly sharpened it works like a dream cutting (actually scraping) very cleanly and give fine whispy shavings. But recently on the damp mulberry it didn't. It was grabby and hard to control.

Clever idea make it convertible! (maybe a socket head screw you could tighten with an allen wrench?)

If the recess in the wet mulberry was across the grain (probably shouldn't be used in end grain!) than perhaps it caught as the end grain came around. Mulberry is ring porous and might be harder to cut there. Sorry, I don't have experience with wet mulberry - I turn it dry.

I suspect that even with your torque stablizer arm it still was trying to rotate. It might be bullet proof if you could mount it on a wider steel bar and cut back a notch for clearance so the full width of the cutter would extend to the left not further than the edge of the support bar. This would work like the swan neck tools so the downwards force at the cutting edge would be directly in line with the tool shaft, a bit like this hollowing tool sold by the other John Jordan (the famous one)...

jordan tools.png

...except the "swan neck" would be formed by the notch in the bar instead of with a bent, curved bar. This would be sort of like the one I ground as well as the one Leo showed.

I made a crude sketch - maybe more notch than needed to clear the face of the blank for that particular angle of the cutter but I had to quit - I suddenly remembered I promised to take a lad out for a driving lesson! The angle of the cutter could be less but the more towards 90-deg the harder it might be to support it well by the tool rest. (Would still need to angle the end back to 80 degrees or so to clear the bottom of the recess.)

dovetail_scraper_dwg.jpg

I might be inclined to hold it with a set screw like that other John guy did or just braze the insert to the modified end of a steel bar.

JKJ

[Brice Rogers]

Thanks for your responses, John.

[Reed Gray]

That can be the wood as well as technique. First, you need a burr on it for good cutting. Honed burr, burr off a CBN wheel, or burnished burr. Second, it works better with a plunge in, then move over and plunge in rather than plunge in and pull sideways. Scrapers can cut fairly cleanly plunging straight in because the wood fiber supports itself, if that makes any sense. You can clean up the bottom of a bowl fairly well with a scraper sweeping across the bottom which is a very light cut, but try to come up the wall, and it doesn't cut cleanly at all, which would be like pulling side ways with the scraper. I have only had one or two pieces of mulberry. Can't remember, but I think it is more stringy than Osage. Some woods will cut better wet, some cut better dry... Even if they are from the same tree or same species and different trees, there can be huge differences...

robo hippy