KICKBACK! (what U don’t know CAN hurt U)
Having perused the various sections of this forum and searching for the term “kick back” and then “kickback”, I couldn’t find any messages on the subject. New To Woodworking seems to be a logical place to discuss the subject so here goes – in hopes of saving someone some grief – and a body part or two.
I’d rate the shaper, spinning a 5 pound, 7″ diameter head – with KNIVES! – the scariest power tool I use – rarely. I’m REALLY careful when I use that thing, in part because of the amount of wood it chews off and because I don’t use it often enough to feel confident, but not complacent, with it.
The tables saw? Well that’s the one you have to be careful with. Because it gets used so often it’s easy to become careless – and that – to paraphrase Martha, “Is NOT a good thing”.
Now the obvious No No with a table saw is getting your hand or hands in harms way. But that’s obvious and intuitive. It’s that “kickback” thing – the flying wooden missile that can go through flesh and bones, as well as the connective tissue between them – that you hear about and really want to never experience.
There are plenty of “rules” to minimize the likelyhood of experiencing a kickback and some conflict with each other. And remembering a bunch of rules each time you use the table saw is kind of a PITA. I’d rather understand the simple physics of kickback and from that be aware of what nasty forces I need to control. Went so far as to put up some web pages about it – initially for my own use – and now maybe to hlep others understand what can lead to a kickback and how to reduce the likelyhood of experiencing a kickback.
http://home.comcast.net/~charliebcz/KickBack1.html
Hopefully others will share their observations and suggestions. The goal is to save a person or two some grief.
charlie b
Replies
Admirable aims charlie, where anything that can help reduce the chance of woodworking related injuries is beneficial.
I think you could add to it by including discussion in the use of the European style short rip fence. Also you might mention use of the crown guard in general, but in particular, in conjunction with a riving knife as a means of reducing the likelihood of fingers, etc., coming into contact with the blade.
I cannot deny that, along with Barb Siddiqui, I was one of the authors of the linked item. Slainte.
Richard Jones Furniture
Thanks for bringing up The Long Fence vs The Short Fence question.Euro fences tend to be short - just long enough to extend a little past the back of the saw blade when the blade is at maximum height. Some can be shortened for shallower cuts. U.S. Market fences are ALL long, extending all the way to the back of the table saw’s table, some even locking back there as well as in front.When you think about it, beyond the back of the exposed blade PLUS the distance to the riving knife, which keeps the kerf open, there really isn’t any need to keep the stock behind the blade against the fence. In fact, if the piece being ripped Wish Bones (I.e. Opens up like a “Y” ) it can push against the fence behind the cut and try to move the whole piece of stock being ripped AWAY from the fence and bind against the blade. In an extreme case, it could push the riving knive out of alignment with the blade enough to allow the stock to contact the blade’s rear teeth - the ones that typcially initiate a “kickback”. OR - it could try and push the end of the fence away from the blade - also not a “good thing”.Now let us examine The Short Fence vs The Long Fence from a leverage perspective. And let’s begin with both fences locked down only at the front of the table. If you apply one pound of force to the end of a one foot lever you produce one foot pound of torque. Apply the same one pound of force to the end of a two foot lever and you produce TWO foot pounds of torque - twice that of the one foot lever. Now if you’re tying to lift something, the longer the lever arm the better. BUT - if you’re trying to keep the lever from moving, which is what you want to do if the lever is your rip fence, LONGER ain’t better at all, SHORTER IS BETTER. Kind of obvious when you think about it - right?OK - so what if we can lock down BOTH the front AND rear of the fence? Well if you look at it from a Moment Diagram perspective - forces applied to lever arms, The Short Fence vs The Long Fence Locked Down At Both Ends is about a push - basically they’d work the same.BUT - what’s it take to lock down both the front and rear of the fence AND keep it parallel to the blade its entire length? If the back locks down before the front, or the front locks down before the back, you could cause the fence to go out of parallel with the blade. If the front of the fence is closer to the line of the blade you’ll bind the stock against the outside of the saw blade. If the front is farther from the line of the blade you’ll bind the stock against the inside of the blade. Neither situation is desirable.ALL the mechanisms to lock the front and rear of the fence down together and parallel to the saw blade introduce one more critical set up requirement - AND one more thing that needs to be checked periodically and adjusted if necessary. Don’t know about you, but I’d rather spend time cutting wood rather than checking and adjusting things BEFORE I can cut wood.I can only think of one reason for a longer fence - a place to attach Hold Downs behind the cut - Board Buddies, magnetic Draw-Tite etc. - all keep the stock down on the saw table and some also pull the stock into the fence. You don’t want the stock behind the blade coming up off the table - and perhaps into those spinning teeth rising up out of the table top. It’s those rear teeth that raise all the hell. ANYTHING that can cause the stock to come in contact with those rear teeth is “not good”. The Rear Teeth ARE BAD!So what say ye?Newer Newbies - are you listening?charlie b
charlie, I think that for almost all rip cuts the long fence is the ultimate pain in the arse. The single most effective means of reducing the chance of kickback during ripping operations, I believe, is to fit a short rip fence to a saw-- the Delta Unifence is a copy of the type common in Europe. This really ought to be followed up by using a riving knife and a crown guard, although a US style splitter is better than nothing at all. Use of the long rip fence has many disadvantages as outlined in the article I provided a link to earlier so I shan't go back over that discussion.
Rather, people can click on the link, read it, absorb the information and choose how they want to use a saw. If they decide after reading what's there that safer saw operation is not for them, it's no skin off my nose. There are times when a long rip fence is handy.For example they can be used as a sort of substitute for a spindle moulder (shaper) and as replacement for a router incorporating use of the dado blade-- I never use a saw this way as there are much better machines for doing this kind of work. (Incidentally, for anyone that is wondering, I lived and worked as a woodworker in the US for ten years and know in great depth the woodworking practices common in both Europe and the US.)
It's good to see that Powermatic and Grizzly are taking tentative steps into the post World War Two years (never mind the 21st., century) by offering saw models with riving knives and crown guards. With a bit of luck for American saw users and buyers, perhaps 20 years from now, the US saw companies might even hesitantly bring their machines up to early 1970's standards, ha, ha. Slainte.Richard Jones Furniture
Richard,Being raised and prejudiced American style, I must say that the short fence is very interesting. I see a retrofit in my future.I notice your fence is to the left of the blade in your photos. Are you left handed or is that the European preference? It looks to be awkward 'pulling' into the fence as opposed to 'pushing'.Just one more thing, what is the slot in the run off table for?ThanksAndySaid least is often said best,
but said best is often said least.
Andy, are you sure about that? All fences are to the right of the blade as you feed the wood for ripping, and it is on the saw in the article my link sent you to. Slainte.Richard Jones Furniture
My bad. At first glance it looked as though it was reversed.So what about that slot?AndySaid least is often said best,
but said best is often said least.
Andy, I see this thread has popped up again after a period of dormancy, and also see I missed to answer a question you posed, which was, "So what about that slot?"
So, if If you're still watching, I think you're referring to the slot you can see at the front of the table that runs horizontally underneath the table top.
The answer is that the extension is draw-leaf which slides out from under the main table top to support ripped offcuts. It slides under the main table top when closed. In its closed position the leaf fills the slot I think you're referring to. All draw-leaf tables operate in the same manner revealing a gap under the main table top when the leaves are extended. It's just that in most cases you don't see the gap because the leaves and the top typically overhang the table framing parts by a few inches. That isn't the case with this table.
Sorry about missing your question in the first place, but I hope you pick up this answer. Slainte.
Richard Jones Furniture
Edited 11/25/2006 4:49 am by SgianDubh
Richard,Still watching. After a closer look at the side by side photos I see the draw-leaf that would fit into the slot. And that slot in the end of the runoff table is indeed the one I was referring to.Thanks for the answer at long last.AndySaid least is often said best,
but said best is often said least.
I'm American, but not prejudice. I picked up on Sgain's short fence about 3 years ago and tried it. After about 2 hours of ripping throw aways to get use to the different feel at first, I wouldn't be without it as I feel it is more of a contribution to the safety issue than even the riving knife and crown guard. And I would prefer not to be without those either.
As far as retrofitting, I made one that slips over my fence in about an hour. Moves forward and backward for various depths of cuts with quick release lock down bolts secured to fence. It also comes off the regular fence in about 30 seconds when I use the fence to rip mid-size panels.
BTW.. you could just clamp a face on the regular fence and you got a short fence. Life is simple...
Regards...
SARGE..
It's the simplest things that make the most sense. I was trying to figure out a way to remove the teeth only on the backside of the blade, but I was losing too much sleep over it.I was tongue in cheek when I said I was prejudiced. I'm sure you knew that though. I was just playing the ugly American for Mr. Jones sake. He has spent time among us and seems happy to be home. Though maybe the ugly American is getting too much press lately.AndySaid least is often said best,
but said best is often said least.
Doing so won't prevent kickback on a TS, but the smartest thing you can do when learning to use the machine is to train yourself to stand to one side or the other of the blade. That way, when a piece kicks back and takes flight, at least it won't hit the operator.
Happened to me just the other day.
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"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
If you have a "Flip & Fly" there is no safe place to stand, other than BEHIND the saw - which poses a much greater threat of injury than a "kickback". This type of "kickback" typically occurs with cross cuts of smaller stuff. the cut off on the fence side rotates into the back teeth of the blade - the ones coming UP out of the table - the ones that'll lift the cut off UP and then onto the spinning teeth above. From there it's Duck and Cover cause the piece will go airborne VERY quickly - and in a totally unpredicatble direction.The best safety device for a table saw, IMHO, is a euro type riving knive that sits close to the blade over the top rear quarter of the blade - unlike "splitters" which are close to the blade - but only when the blade is fully raised, the gap between blade and splitter increasing as the blade height is reduced.As for the blade guard - I personally want to be able to see the blade cutting. AND I want to be able to control the stock on BOTH sides of the cut. None of the guards I'm aware off meet both criteria. The "clear" plastic / lexan/ polycarb versions get dusty and scratched up to the point where they're essentially opaque - including the ones with the over arm dust collection. And should I ever have an exploding wood incident on the table saw, the last thing I want to worry about is a bunch of flying polycarb or metal, even if it's only aluminum. Others may differ re: not using the blade quard. To date, I've still got all my original issue body parts - hair being the exception - but that's not the table saw's fault.For newbies, I think setting up the table saw properly is often overlooked - seldom if ever mentioned in the "users manual". If the blade isn't parallel to the miter slot then cross cuts can be dangerous. When ripping, if the fence isn't parallel to the blade it can be dangerous.Any more table saw safety tips for newer newbies?charlie b
You are so right. My solution to crosscut kickbacks is a sled. It is so much safer as the material stays on the sled which passes the saw blade, and isn't free to ride against the blade. It's easy to set a 0 tolerance between sled and blade, so nothing drops between the blade and sled, so nothing to propel. I do all my crosscutting with a sled, and can't do with out it.
That is probably the most important point on kickback that i have heard. After getting smacked with a piece of knot coming off the back of the blade, I have made it a constant rule to me, that I NEVER stand in line with the blade. So far so good.
Charlie, you must have been sucked in by the virtually useless "Search Messages" box at the bottom on the left. No joy there. Doing an Advanced Search (upper left-hand side). Got 199 hits on kickback.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
A little off the subject but still relevant. Kickbacks and other flying debris, Anticipation and preparation is the Key. Just yesterday while turning a Goncola Alves bowl (7" dia.) There was an unseen shake crack in the stock and a big chunk flew off and wacked me in the face shield. Always think safety and be prepared for the eventual, That dagger shaped chunk could have easily taken out an eye. Good thing I always wear a face shield and safety glass while turning.
Work Safe, Count to 10 when your done for the day !!
Bruce S.
Edited 9/14/2006 10:02 pm ET by BruceS
Hey Charlie:
Have been a part of and observed more than enough kickbacks, great placement in this forum for your writing.
I enjoyed it.........THANKS!!
I always feel the best deal is to stack the odds in my favour, and to this end use any means at hand to stay safe. The short fence on the saw table is a must, work cannot be held to the fence after the cut is made. By all means install a long fence and support table in front of the blade. Use a splitter and make a new one for each blade thickness.
The enclosed photos show the hold down I use on my 20mm Kity spindle and saw fence if there is any risk of offcuts coming back. It basically is an auto ratchet bearing a wheel and tyre which, when clamped to the table, locks at the first thought of throwback yet allows the work to pass the cutter easily. The thick mounting plate can be clamped flat or vertically to the fence.
I tested it by spindling some oak with a nosing cutter block hand feeding and then letting go. The ratchet locked and the moulding was not damaged. I submitted the idea to a mag. but had no response.
Interesting device. When used on a rip fence as a hold down and anti kickback device it look like it would be quite effective. In that mode, it functions like a product called Board Buddies, wheels with axle/shaft attached to the fence, wheels on the top of the stock being ripped and the wheels turn only in the feed direction, locking when the stock tries to move back towards the infeed direction.If you flip the images "upside down" and imagine it clamped to your rip fence, the "L" bar stock shown in the first image being the saw table top, it's more apparent how this thing works.Now about terms and definitions since Yanks and Brits/Auzzies have different terms for the same thing, or just different spellings - miter/mitre, rabbet/rebate, board/timber, etc.. So I'm guessing that your 20mm Kitty "spindle" is either what we Yanks call a 3/4" bore shaper or what we Yanks call a router and the 20mm, which is a bit over 3/4", is a router bit. In that mode, it's not clear, to me at least, how your device would be used. Pics in use?charlie b
I have those problems also. It's a spindle moulder, or shaper to you. Uses french head cutters, circular cutterblocks or profiled cutters but 20mm bore not common now.
The point is that the base is just plywood, so I can make them to suit the task and transfer the working arm between them as appropriate. So long as the pivot pin is substantial the whole thing is really sturdy, I always felt the Board Buddies were a bit on the light side. The wheel is 3/4 ply with a square hole, pressed on the ratchet drive and carrying a tyre made from a plumbing fitting. The spring was from an Anglepoise lamp.
It is very effective. For kickback to happen the work has to move a certain distance to allow leverage to overcome the feed or hold down force. By using a quality (but old) ratchet with fine movement inside I find there is practically no work movement. Of course the clamps holding the base down to the work table have to be good.
I am some six hours ahead. If I get time tomorrow I will try an action photo although presently the Kity is set to cut mortice cheeks.
Thank you for the interest. David
You're still using french head cutters on that Kity, mufti? I haven't seen one of those in use for over 25 years now.
Banned, illegal, and dead as a dodo in workshops where there are any staff and HSE might pay a visit. Mind you, I've still got slotted collars and Whitehill blocks hanging around that can be pressed into service when the HSE's not looking, ha, ha-- ha, ha, ha.
However, I'd draw the line at firing up an old square head cutterblock-- the noise alone as they gather speed is enough to make most users crap their pants. Slainte.Richard Jones Furniture
Perhaps I should call myself Dodo. They get used on small repairs etc which are done for free, and I wear body armour and a riot helmet.
I just cannot understand the American approach to safety. We get Norm tapping his eye protection, and then making trenching or ripping cuts without guards and with overlong fences which are supposed to be advantageous! A bit like developing a carbine round that does not create a shock wave on entry so the exit hole is the same size. A clean death, but it goes on to kill the ten people standing behind the target. On the other hand the building codes mentioned in FH seem to be better than ours.
Live long and prosper.
mufti,
Didn't know they allowed carbines or ammo in Limeyland anymore. I believe that the thinking re full metal jackets has to do with one of the Geneva convention articles- at any rate, soft point ammo is prohibited. Of course, in combat I suppose wounding the ten poor fellows behind your target might not be thought a disadvantage.
Then again, with firearms as with tablesaws, (just to get back on topic) a safety (device) is only as effective as its user. An acquaintace once pointed out about HE artillery shells, "They're perfectly safe...until you forget how dangerous they are."
Cheers,
Ray
This is it, but posed shots since I do not wish to move fence settings. The first should show plastic strip used to hold work before cut starts. The spring is just slack. Then as the work passes cutter the ratchet swings on the pivot against the spring and keeps the wood against the fence. The cutter block is the one used with that fence, hence the cut outs.
Normally I also use a top guard coming through the hole above the cutter block, and then you cannot see much. I have just realised I did not resize these photos, I hope they are ok!
I like to kick back, usually a cold one after a long day, works for me.....
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