Unintended asymetric turning

Piece of cake!

Once you've used soft jaws with success, you'll wonder how the hell you got along without them. They are, truly, the magic bullet of lathe work.

I use soft jaws in place of the hardened steel jaws with almost NO exceptions. I have a set that is bored through for gripping bar stock. It runs truer than the factory jaws in both concentricity and perpendicularity.

Harold

Reply to
Harold & Susan Vordos
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The only problem I have with that concept is that you often get advice that isn't very good, and if you are asking the question, you may well not be able to discern good suggestions from those that are troublesome. I face this problem all the time with well meaning but poorly informed people that think of themselves as machinists (yet they have no experience in the trade. Strange!)

In many cases, they've struggled through a tough project and succeeded to some degree, but don't have a clue that there's much better ways to approach the problem. There's nothing quite like years of experience, especially if they're spent running a (commercial) shop, making all of the decisions.

The biggest problem you'll face on an open discussion forum such as this is the guy that can't resist telling you how to do a job when he doesn't know, himself. I think it's a guy thing! :-)

Some guys just love to see their name in print.

Harold

Reply to
Harold & Susan Vordos

Sure, but they may scratch the finished surface.

jsw

Reply to
Jim Wilkins

So, no different from other spheres of life then...:-)

Reply to
mkoblic

Thank you. Read and bookmarked. Very helpful not just for the specifics of soft jaws but also for the general principles.

I re-read all the posts in this thread as well as a thread on another forum dealing with a similar problem and came up with an idea which:

1) Might solve the problem to some extent 2) Will not tax my limited skills 3) Will not tax my bank account

Following the principles of the soft jaws and the step collet I thought of attaching a 5/8"+ thick aluminum plate to one of my faceplates, turn it true and face it. Then turn a recess in the face of this plate with the ID=OD of my work piece (well, a slip fit). Clean the inside of the recess as well as the work piece and attach the work piece inside this recess with double sided sticky tape. This should allow boring ID and facing of one side of the work piece. If all my future pieces are turned to exactly the same OD and the face plate-aluminum plate assembly is kept intact this setup should allow repeat work.

To be honest I think it was George McDufy who touched on this solution but did not expand on it.

Meanwhile I shall explore the possibilities of a 5" chuck with two-component jaws.

Michael Koblic, Campbell River, BC

Reply to
mkoblic

Thanks Harold, it's a pleasure reading your concise descriptions and recommendations from your experience in various aspects of metalworking.

Reply to
Wild_Bill

Thank you, Bill. I appreciate your kind words, but, most importantly, that you found value in my comments. There's a lot of expererience backing those words! :-)

Harold

Reply to
Harold & Susan Vordos

While the concept appear sound, I think you'll find it doesn't work well. For one, when you start machining, you'll generate heat---which softens the adhesive somewhat. You will be very limited to the amount you can remove per pass.

As you face material that has not been previously machined, upsetting the surface tends to relieve internal stresses, causing the material to move. That, couple with the generated heat and the pressure of the cut will most likely pull the part from the pocket.

Not suggesting it can't work, but I truly believe you'll just exchange one set of problems for another set of problems.

On a positive note-----many years ago, where I was trained as a machinist (Sperry Utah Engineering Laboratory), we were the builders of the Sergeant Guided Missile. The missile had brakes! (Really!) Being a ballistic missile, and solid propellant, brakes controlled the trajectory, with an onboard computer (that used ferrite core memory). Anyway, the bulkhead on which the brake system mounted was a large magnesium truss. While tolerance wasn't really tight, it was difficult to accomplish because the truss was easily deformed by holding devices. In the end, in order to maintain the level of precision required, the faces were held to the mill table with double sticky tape. Needless to say, cuts were VERY light, but it provided the required restraint without distorting the part. It can work, but it's very labor intensive.

Can you be a little specific and tell me exactly what you're trying to accomplish, and how you start? Type of material, thickness of material, destination sizes and tolerance, and anything that may flavor the outcome would be nice to hear. Could be I can offer a solution----or not! :-)

Harold

Reply to
Harold & Susan Vordos

You may be remembering a similar custom wooden chuck from Holtzapfel. There or somewhere I saw a variation with the outer lip slit and undercut so a large sliding steel ring (hose clamp?) would wedge it closed on the disk. I think he suggested a mix of pitch and wax, available now as cross-country ski wax, to further hold the disk. I use hot melt glue for such tasks, melted with a hot air gun or hair dryer. So far it's held as long as the work doesn't become too hot to touch.

My large thin disks are gear or pulley blanks which can tolerate extra mounting holes, and I have 5C pot collets to hold them.

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This (see?) second-hand pot collet had been pretty much used up for custom jobs, so I refurbished it by boring the inside smooth and turning a matching plug on the side of a thick aluminum disk. After tapping the aluminum and screwing it to the collet I sawed it into sections. The steps I've cut are as shallow as 0.020", to hold thin spacer washers.

Some of the older pot collets have a solid shank and a tapered closer ring at the OD like the wooden chucks. I'm trying to think of a way to mount an inside-tapered ring on a face plate such that it would force pie jaw plates inwards as you tightened them against the faceplate. Perhaps a large tapered pipe thead like a drain pipe cleanout plug would hold square while closing the jaws.

jsw

Reply to
Jim Wilkins
[...]

I can't argue with that. Also cannot pretend that it was an original idea...

[...]

I don't think I can add much to the OP. The end result should look something like this:

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Tolerances? If it looks right it's close enough...:-)

Michael Koblic, Campbell River, BC

Reply to
mkoblic

Holztapfel would be the original reference. There have been at least a dozen suggestions elsewhere for variations of the same: Many use wood (MDF seemed particularly popular) and hold the piece variously with wax, pitch, shellac, hot glue, double-sided sticky tape and superglue.

I have a problem with using wood: The sacrificial plate would have to be turned on the metal lathe to get the centering just right and that would create an unholy mess. I thought aluminum would be a reasonable compromise. My concern with pitch, wax, hot glue etc. was that you have to get a definite layer of the adhesive between the piece and the plate. Making sure that it lies flat against it would be, I imagine, difficult to achieve. How did you manage it yourself? I have tried the double sided sticky tape in other applications and thought it an advancement on an old idea.

OK this would be what others called a "step collet"?

That is getting too clever for me. Which is where the double-sided sticky tape comes it :-)

There seems no doubt that if one did a lot of this the pie jaw solution is the best one. A better 4-jaw chuck follows some way behind as, if I am correct in diagnosing the problem as flexing of the part, it would not really solve the problem. I am told that my lather is too small for 5C collets but looking at this it may not be strictly true:

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Either way, not much change from $500 when all is said and done, pie jaws or 5C collets.

Fortunately the issue is neither critical nor time-sensitive.

Michael Koblic, Campbell River, BC

Reply to
mkoblic

That part screams for soft jaws. Trust me!

Harold

Reply to
Harold & Susan Vordos

Nah! If you don't have a dust collector, think Shop Vac, Mikey. Catch it at the tool and there is no mess. Dust collectors are quite quiet, while most shopvacs are noisyassed beasts. Your choice.

-- Small opportunities are often the beginning of great enterprises. -- Demosthenes

Reply to
Larry Jaques

Larry Jaques fired this volley in news: snipped-for-privacy@4ax.com:

Larry, you'd have to do a quite workman-like job of collecting that dust. Wood flour is the bane of metal machinery. It's also damned hard to collect all of it with a vacuum cleaner -- there's just not enough volume OR large enough cross-section of moving air to catch all the fugative dust. That job really requires a high-volume dust collector.

Nahh... I don't like wood on the metal lathe, either. Were it me, I'd be backing that thing up with a sheet of type I PVC -- something I can glue to effectively, then later dissolve or de-bond.

LLoyd

Reply to
Lloyd E. Sponenburgh

I turn wood, plastic and rubber on my metal lathe. It helps to pick a depth of cut that makes reasonable-sized chips, not huge ones or dust.

Wood chips vacuum up easily. They might cling to grease but not way oil, which they absorb. Just yesterday I adapted a 3/4" flex tube to a vacuum cleaner to reach into narrow spaces, in this case the bell housing of my truck which chipmunks had filled with acorns after I screened off the air cleaner inlet.

At several jobs they had added a short garden hose etc to the shop vac to clean out tee slots and other recesses on machinery. The narrow radiator attachment is too long and awkward and the others are ineffective.

Heat the work hot enough to melt the glue and press it firmly in place with the tailstock center.

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check for runout.

If they have steps. Photos load very slowly on dialup so I take the first one that's close.

The collets I have were originally flat-faced disks, like the Microcentric pie jaws in my photo. They were machined to hold specific parts, then re-used for larger ones, until they were used up.

I haven't needed to make top jaws for my 5" Bison 3-jaw, but on examination it doesn't look too challenging as long as you true the clamping surface in the lathe. You can remove the inner jaws to test the fit without removing the new top jaws from the milling vise, and shave down the backs to barely clear the chuck body afterwards. The crosswise tenon engages before the radial slot, so you can fit each individually. I think you could get away with a loose fit for them, as clamping the work will take up the slack. However the Bison ones were - very- carefully fitted and are marked with the chuck serial number and jaw 1, 2 and 3.

This chuck is fully 6" from the end of the mounting plate to the jaw tips, which eats up a lot of work space and could be too much overhang for a lathe with a thinner spindle.

A better 4-jaw chuck follows some way behind

For me 1 minute of video takes >10 minutes to load.

I suggested Holtzapffel to you because it's full of ways to save that $500, and he was also chucking ornamental objects that scratch easily, which is really the reason for wood jaws.

I think the best way to get 5C collets is to buy a lathe made to hold them in the spindle. They are more useful for high precision like optical or hydraulic parts than for general use. I still do a lot between centers or on a faceplate.

jsw

Reply to
Jim Wilkins

Wood flour is created by -dull- tools. Keep 'em sharp and you get shavings which are much larger in crossection.

-- Small opportunities are often the beginning of great enterprises. -- Demosthenes

Reply to
Larry Jaques

Larry Jaques fired this volley in news: snipped-for-privacy@4ax.com:

Fire and smoke and burned cut lines are created by dull tools. Wood dust can be caused by an exquisitely sharp tool taking fine cuts. Wood flexes a bit under cutting pressure. When it recovers from the first deep cut of the tool, it gets lightly shaved by subsequent passes. Even a properly- adjusted (and sharp, and HONED) surface plane produces a combination of nice curls and fine dust; not _much_ dust, but some.

Cutting lightly against the backing would have that effect. So, are you recommending he cut hard and full against the backing piece on every pass? What about when he stops the feed. Does that last tenth the tool takes off after it stops moving count as a "fine feed", or no?

I'm a so-so home shop machinist, but a _very_ competent furniture maker. There's not much about the machinability of wood (from the common to poisonous exotics) you could teach me. And I'll hold to my first -- wood particles of quite nearly any size are persona non grata around metalworking equipment. Even _shavings_ will absorb oil.

LLoyd

Reply to
Lloyd E. Sponenburgh

OK, 99.6% shavings, 0.4% flour. But fine dust is most easily picked up by the dust collector (if you have HEPA sub-micron bags.)

Oui.

OK, I catch your drift, but on a limited basis, a bit of wooddorking on a metalworking machine won't do it any harm. Just wipe and reoil the ways afterward if you need to. How much harm does wood do to the ways, anyway? It's MUCH softer than iron/steel. Bamboo (seldom machined) has lots of tough silicates, but most wood is primarily a soft cellulose.

-- The art of life lies in a constant readjustment to our surroundings. -- Okakura Kakuzo

Reply to
Larry Jaques

Maybe the results depend on the species of wood. I use red oak and see hardly any dust, either turning or planing. And my lathe has felt way wipes.

How did pattern makers manage wood on metal lathes?

jsw

Reply to
Jim Wilkins

If you ask a male golfer how far he hits his driver the answer is never less than 240 yards.

If you ask a fellow 9x20-er if his pieces chatter the answer is never. Under any circumstances!

When I had issues with the finish of my disks I was sent photos of similar items to show me "how to do it". The finish was worse than mine :-)

Indeed. Many do have them.

But then a 4-jaw independent would defeat the purpose of the pie jaws.

I have learned some of that, not being able to go lower than 150 rpm. In fact the differences from tool to tool can be striking. I am still struggling with consistency.

Oddly enough the finish matters less on these pieces: Some get a brass face anyway which covers a multitude of sins underneath, others get sanded anyway as I found that unless the face is absolutely smooth, the transfer of patterns is only partially successful.

As Harold is about to say: "Only if they have two-piece jaws".

And yourself.

Michael Koblic, Campbell River, BC

Reply to
mkoblic

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