has this happened to you

[hughie]

My teknatool screw chuck and the chuck part company the other day much to my surprise as it has never happened before. On closer inspection it looks like it had fractured sometime previously and this was the last straw.


This little block of Deadfinish has dia of around 120mm secure with the tailstock as I normally do when roughing out on the screw chuck.

I've got another somewhere, but I am tempted to make another myself with a bigger core diameter of around 10mm as opposed to the original of 8mm and probably add a few radii where they had square shoulders etc.

[Mobyturns]

My teknatool screw chuck and the chuck part company the other day much to my surprise as it has never happened before. On closer inspection it looks like it had fractured sometime previously and this was the last straw.

That is why I have maintained that some turners who use screw chucks on large bowl blanks with high speeds in a public demo setting are very dangerous people! :((

Strength of materials again, may have been a QA issue with a flaw in the material, or manufacturing, just normal wear & tear, or abuse. How often do you use a screw chuck on a blank with an uneven mating surface to the faceplate or chuck when using the screw chuck? Each time you flex the screw out of alignment you are weakening the material & creating micro stresses in the material, it will eventually fail! Don't get me wrong they have their place and are safe to use when used appropriately.

The old excuse - it has never happened yet - is a pretty poor excuse, it does happen & it is predictable & known about, its just that its not publicised, so turners do not hear of it often.

[sjm]

Can't say it has, but I'm not surprised. I guess I'm over cautious, because I drill a slightly undersized hole and then have to really wrench it tight to screw it in. I guess one of these days it will shear right off.

[hughie]

Strength of materials again, may have been a QA issue with a flaw in the material, or manufacturing, just normal wear & tear, or abuse. How often do you use a screw chuck on a blank with an uneven mating surface to the faceplate or chuck when using the screw chuck? Each time you flex the screw out of alignment you are weakening the material & creating micro stresses in the material, it will eventually fail! Don't get me wrong they have their place and are safe to use when used appropriately.



Its done a fair bit of work, so I doubt QA, probably me pushing it :U. I do have a couple backing plates I use when turning larger diameters to back up the screw chuck.

But looking at it I reckon it could be improved upon design wise also use a different material. Making my own here would mean not being constrained to make a profit. But I am fairly busy at this time of year so it may not get done.

[ian thorn]

I have seen it on a club lathe

[Wood Nut]

:oo:Hi Hughie,

This certainly is a timely reminder to those of us who become complacent from time to time. If this can happen to an experienced turner such as yourself, then what about novices/learners. They may not realise the importance of using the tailstock early on when roughing down, although this could have happened at any time after removing the tailstock.

I won't go into the physics, but even a piece such as this, doing 1000 rpm could have a lineal velocity that would be scary, not to mention the energy tied up in rotational motion. The irony of using 'deadfinish' does not escape me. Having EVS control as on your lathe is also much safer for those who are a bit slack about changing speed manually.

A novice turner at our club had a large unbalanced block on a centre screw/parallel screw etc but turned on the lathe without checking speed or bringing up the tailstock. The lathe, although having EVS, was left on a high speed. The end result: one flying mass that went through a lexen screen, a screw that bent by about 35 degrees and a massive influx of adrenalin from all those close by.

Cheers mate and see you soon,
Paul

[Tony Morton]

Hi Hughie
About ten years ago I had two brake in a week they were from Carba Tec one was brand new the other had been around for a while ,I believe the problem was that the hole wasn't drilled true to the face of the blank and when tightened this caused some stress and eventually snapped.
Cheers Tony

[hughie]

[About ten years ago I had two brake in a week they were from Carba Tec one was brand new the other had been around for a while ,I believe the problem was that the hole wasn't drilled true to the face of the blank and when tightened this caused some stress and eventually snapped.


Thats highly likely and or as it pulls up to the blank its skewed off square. Further to my woes I glued a block left it over night and darn thing come apart as well :U Comes of being in a hurry and not giving enough attention to the details

[Pat]

Neil, I bent a Woodfast screw and mentioned it at the club, just in time for one of the boys to tell me that a machinist mate of his, was going to make him a 25mm screw chuck and would I want one. I can supply some pics if you want, it's very hard to bend or break the screw.:;

[hughie]

Neil, I bent a Woodfast screw and mentioned it at the club, just in time for one of the boys to tell me that a machinist mate of his, was going to make him a 25mm screw chuck and would I want one. I can supply some pics if you want, it's very hard to bend or break the screw.:;

Absolutely Pat I have a design for a slightly bigger one, but 25mm sounds the way to go.

[gtwilkins]

Hughie,

Yes I had it happen to me with a Teknatool screw but I was using it in my Vicmarc chuck when it happened. Broke in the same place and I also had evidence of a stress fracture or previous crack.

I had never abused it and always had been careful to use the tailstock and had never spun really huge chunks as I have the rings for that

I suspected a stress fracture from when the threads had been rolled.

Trevor

[orraloon]

I dont use mine a lot and only on small stuff when I do. Guess I,ll be using it less now after seeing that.
Regards
John

[Pat]

Some pics239018239019239020239021

Apologies for pic quality, I am a worse picture taker than turner.
Mine is M30x3.5 bolt welded to 65mm bar that has been turned down leaving a minimum 23mm shank.

Drill a 25x25mm hole with a forstner bit

[dennisk]

I dont know if you guys down unda have Oneway stuff but I use the Stronghold chuck(the only one that would fit on the 1 1/2" headshaft )and I use the screw that came with it, the 1 1/2" Woodworm and it works a treat! I just did this platter on it to get the bottom ready for a chucking recess. Its 14" in diameter and I was running it at 1650. Jimmy Clewes taught me to turn fast and it works. I just entered this in the monthly comp on UK workshop. Its done in mahogany and ash.

[NeilS]

Neil, I bent a Woodfast screw....

I've snapped quite a few of the smaller diameter Woodfast screws, but none of the Vicmarc or Novas, yet.

I agree that drilling off square to the face of the blank is the cause. The flexing of the screw as it is pulled tight against the blank eventually fatigues the metal. It's just quicker to drill the hole freehand than use some sort of jig to keep it square. While in the workshop by myself I can justify doing it that way. In company I would need to use a fresh screw and do it properly!

[Tim the Timber Turner]

I've abused a Glasser stainless steel thread for 20 years and never had a problem.

Cheers

Tim:)

[RETIRED]

Same here.:cool:

[gus3049]

NOT YET!!!

But I use it all the time. I have a Versa Chuck and the screw that comes with it is pretty substantial. I can't remember the last time I used a faceplate although I don't often turn stuff much bigger than 12" diameter. I ALWAYS use the tailstock though, even with small stuff.

After seeing that, I will double check the squareness of the hole a bit more carefully.

[NeilS]

I've abused a Glaser stainless steel thread for 20 years and never had a problem.

Cheers

Tim:)

In case anyone is trying to track one down (I found it quite hard to do so when Tim & recommended it in an earlier thread (http://www.woodworkforums.com/f8/chuck-screw-problem-156941/index2.html#post1537038)), here it is Glaser Hitec Screw Chuck Replacement Screw 3/8" (http://www.glaserhitec.com/shop/shopping/glaser-screws/) , but just the screw component.

The standard spindle threads that the Glaser screw body is manufactured in doesn't include our 30 x 3.5mm size. So, some boring may be required to retrofit the screw to one of our standard faceplates.

I've yet to order mine, so if anyone else wants me to add a few extra let me know. Depending on what shipping method they insist upon (courier costs are much higher than standard US post) there may be no advantage in batch shipping such a small item and it might be just as easy for individuals to order directly from Glaser.

[Pat]

The standard spindle threads that the Glaser screw body is manufactured in doesn't include our 30 x 3.5mm size. So, some boring may be required to retrofit the screw to one of our standard faceplates.

Neil, couldn't you get a chuck insert from Vicmarc/Vermec/Nova, if Glaser are M33x3.5? The actual screws look like they are set screw239083 retained, not screwed in like the Woodfast screw chuck.

[Tim the Timber Turner]

The easy option is to purchase a Vicmarc 3 in 1 screw chuck.

These use a Glasser screw and give you 3 sizes of backing plate for the screw..

From memory around 100 bucks.

Cheers

Tim

[RETIRED]

The Woodfast screw chuck also uses a Glaser type.

[Tim the Timber Turner]

The Woodfast screw chuck also uses a Glaser type.

Tha'ts interesting .

I've never seen a glasser type Parallel thread screw on a Woodfast chuck.

Is this something new?

Any chance of a photo?

All the Woodfast Screw chucks I've seen have a screw in type screw.

This screw was the week point of this chuck, they used to snap real easy.

I would hazard a guess and say that this screw was the largest (in quantity) selling spare part that Woodfast ever sold.

Cheers

Tim:)

[NeilS]

Neil, couldn't you get a chuck insert from Vicmarc/Vermec/Nova, if Glaser are M33x3.5?

Pat, I take it that those chuck bodies all have a M33x3.5 internal thread (I don't have one at hand to measure). But, if so, their inserts should work on the Glaser body, although it doesn't seem like that would leave much meat between M33 and the M30 (on most of our lathes) for an insert.


The actual screws look like they are set screw retained, not screwed in like the Woodfast screw chuck.

239083


As Tim said, the later Woodfast screw chucks (which they call a Screw Point Chuck) has the double ended screw that screws into the faceplate. I also have an earlier model Woodfast screw chuck that secures the screw in the same way as the Glaser, but don't imagine there are too many of them about.

Tim - I would say the thread on the Woodfast Screw Point Chuck is parallel; see image half way down this page (http://www.woodfast.com.au/index.php?p=1_8). However, I seem to snap them too often to be worth the trouble.

Hmmm... just spotted their Screw Spigot Chuck (a bit lower down that page) which looks like my older Woodfast screw chuck but with a much larger thread (like a tap) on it. Don't reckon you would snap that one in a hurry! Might be worth a try.

Besides the Vicmarc 3 in 1 screw chuck (thanks Tim), Vermec also sell a replacement screw (http://vermec.tripod.com/PDFs/Screw_Faceplate_M30x2mm_Ball.pdf) for their Escoulen ball thingy, that could be retrofitted to something.

However, none of these screws are made from stainless steel like the Glaser screw, which may be an advantage that is worth the extra $s and trouble, or not.

[ian thorn]

why not just drill it with a 54mm bit and put it on your 50mm jaws. I do


Ian

[NeilS]

why not just drill it with a 54mm bit and put it on your 50mm jaws. I do


Ian

Been there, done that. It wasn't my preferred method.

But, your not alone Ian, others also prefer to do it that way, like Robo Hippy who turns out bowls in the thousands.

At that drill diameter I found I couldn't satisfactorily drill the recess freehand and had to do it on a drill press which then required extra setting up time, given that the backs of my blanks (the bottom) aren't usually flat. If you buy blanks or prepare them yourself with a flat (and parallel) back then that may not be such an issue.

Since I have already drilled a centre-pin hole in the face of my blanks for rounding on the bandsaw, I find it very quick to then just spin the smaller blanks onto the screw chuck and start turning.

Being able to reverse a blank onto the same chuck for turning the inside has its advantages if you are turning one piece at time through to finish. I tend to turn in batches (all the outsides then the insides) so have less chuck swapping, anyway.

I also do all of my bowl turning outboard (without tailstock support) and found the drilled recess method didn't hold onto the blanks any better than the centre screw method or as well as the faceplate method, but am aware that others find it adequate or prefer it.

I think I still have an old Leady (Bruce Leadbetter) expanding chuck that was specifically designed for use with the recess method and probably also have that dedicated 'mortice bit' that went with it; both gathering dust and rust in the bottom of a drawer somewhere...:rolleyes: