# Homemade Table Saw Sledge - Part 4 - Jig to Build Tetrahedrons and Pyramids

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In this build I made a jig which fits onto the table saw sledge with the intent of cutting sides to form a regular tetrahedrons and pyramids of various sizes.  I have to admit that the final jig in the video quickly left the realms of functionality because I based the design on the angles of a two dimensional triangle and needless to say I have now re-discovered Euclidean geometry.  That is to say, the dihedral angle of a three dimensional, regular tetrahedron is not the same as the angle of a two dimensional equilateral triangle.  While all the angles of a triangle equal to 180 degrees and that an equilateral triangle individual angle are 60, the angle between two faces of a tetrahedron is actually 70.5 degrees.  For a  pyramid this would be 109.5 degrees.

I haven't had to use pure mathematics for quite a while and we probably all know that in fabrication and woodworking there are many tricks to avoiding sums.  Had my table saw been one which allowed the blade to tilt, I could have compensated for my error but as it stands the gap left inside the tetrahedron is too wide and would probably require hot glue to join.

When I have time I will add a link to a correct sketch up model and write up a step by step with accurate angles.

In the short term, if you have the time to make one and don't fancy the maths, use an online calculator to work out your angles such as the one in the link bellow!

http://www.slyman.org/m_projects_mathematics_pyramids_polyhedra_intersurface_angle.php?alpha=60&n=4&p=45&submit_pyramid_parameter_calculator=Calculate

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## 17 Discussions

I am kind of new to wood working. Metal is my main material. I watch attentively and scratched my head the whole way until the last second and then like a caveman sat there amazed. IMHO accuracy is everything when making this jig.

This is a great video but using the circular saw without the riving knife and a guard is dangerous. The riving knife is designed to stop the timber knipping the back of the blade and being flicked back at the operator. The guard does what a guard should do protect the user from a sharp rotating object.

11 replies

Thanks for the comment. You'll be glad to here I am planning to put a riving knife on the table saw at some point, but will not be able to fit a guard because the sledge crosses along the blade. However, just to point out, if you look at the majority of re-enactments of accident you will see that the fence is almost always in place and the material is being over worked. It is more likely to get kickback if you work your material into the blade while against the fence while there is almost no risk of that happening on a sledge. Anyway since finishing the sledge, I don't know how anyone uses a table saw without one.

Mmm not sure I agree and neither do the statistics. I attend a lot of investigations into saw accidents as part of my job and none of them could happened if the guard was in place! In the UK in the work place a saw without a guard is unacceptable. The sledge means you are using the without a guard and therefore unprotected. seen too many people with fingers missing to ever go down this road thank you.

What is your job? Can you share where you find the statistics? I myself am only going by the dozen or so re-enactments I have seen online and from first hand spoken accounts and second hand descriptions, some of which happen with guards and riving knives in place because the blade was too high for example. The riving knife is there also to ensure the material doesn't go off course to maintains accuracy and consistency of cut, as well as prevents material being pushed back into the rear of the blade when the fence if off course. What kind of guard are your referring too, because different table saws have different kinds of guards; some being part of the riving knife while other are suspended from an arm. Have you used a sledge yourself? With regards to missing fingers, a guard doesn't prevent someone pushing their thumb into the blade. Using push sticks and other apparatus like a sledge with a stop (something I haven't made) prevents that. The major reason for accidents is often tiredness, lack of breaks, machismo and alcohol. Sorry about the essay, but I feel the more you clarify the more likely I might do something differently.

I am a trainer in the use of woodworking machinery and a health and safety consultant who also investigates accidents! The riving knife is designed to prevent the wood from closing around the back of the blade (where the teeth are going up not down). The fence is a guide not a safety device. The crown guard is a safety device.
Yes I have used many different sledges over the last 30 years, so are good and some are not. Major cause of accidents users not following procedures for safe working. Yes that might be some of the things you mention but it almost certainly involves improper use of the equipment. In the UK to remove a safety device and use the equipment can lead to prosecution. There is a reason for that... its very dangerous and puts the user and others at significant risk. I hope that helps you understand where I am coming from. I have many many years of experience in these matters.

I like how were are basically saying the same thing but stubbornly not agreeing with each other. Anyway as I said earlier you'll be glad to here that I will be added a riving knife to the saw but maybe you can suggest how I should add a guard? I think overall, builders use table saws in very different ways to carpenters. How would the guard be used if a jig is made to cut finger joints for example? It's impossible and you rely on a well made jig to keep you safe. With regard to prosecutions for removing the guard, I think the law is still a bit ambiguous on tools built from scratch for personal use, in a space without the risk of some chucklehead having a go.

Tools for personal use are not the same as those in a commercial setting. You can do what you like at home. However if you cut your fingers off your rather stuffed in terms of practical work..........
BTW we are not saying the same thing. A guard is the only thing that will prevent material flying up and hitting the user and the riving knife is the only thing that will prevent the timber from snagging the back of the blade whether at home or at work.

I'm sorry but you can't simply say there are better ways of making comb joints without actually showing me an example. I come from a practical background and rely on tangible thinking, and not unchallengeable theory which you seem to enjoy justifying with a smug threat of injury. I take safety quite seriously, which might be why I still have all my fingers. Do you actually think I have not thought about how an injury will effect my livelihood and responsibilities? I've not disagreed with the functionality of the guard or riving knife, but I am not convinced by your method of trying to persuade me. It is attitudes like yours, and your scaremongering approach to health and safety which puts youngsters off making, and working with their hands in the first place.

Savvas, I have to put my two cents of support in here for you. Your instructables are outstanding and I have always found your ideas to be well thought out and useful.

I also agree that safety is important, but mindlessly pushing rules is absurd. The best way to be safe is to maintain focus and control as you work. The best way to create is to apply thoughtful inventiveness to the task. I don't see you violating either of those principles.

Woodworking can be dangerous even with a riving knife and a guard properly installed. Maybe we should just outlaw table saws and prevent anyone from building anything. Has England devolved into such a nanny state that they actually prosecute people for removing a guard from a table saw so you can use a sled??? Do they prosecute you for taking off the "Do not remove" tags from your mattress also? I don't see you consulting large scale manufacturing operations, this is an instructable (and a damn good one BTW.) Neurotic obsessions about these safety regulations do not apply.

This is all coming from a person who, based on his own profile, is a school administrator and creates baby blankets and pillows. The conversation reminds of a friend I have who has aspergers. He is not a bad person per se, but he gets hyper focused on minuta and is just out of touch with reality.

Keep doing what you are doing. There are smart, self reliant people out here who understand the risks we take with power tools. We like your stuff and appreciate the ideas you bring to our world.

Also, despite using a sled and no guard for 20 years I also have all my fingers.

Hi you might well have all your digits and I am pleased for you. I have all mine too. I regularly attend scenes of accidents caused by operators of machines not using the protection fitted or have removed the protection. It don't care really if you remove the protection from your machines as long as it does not cause others to by injured.

Great, glad you like to go to accidents, that isn't the point. These forums are to comment on the ideas shared among the community, not go on a wild safety rant as you have done. If you have thoughts on this sled, ideas to improve it, encouraging words, alternative solutions, etc, those are all encouraged and I would even welcome them from you.

On the other hand this is not the place to stand up on a soap box and demonstrate your need to lecture people on safety. There is a term used for for people posting as you have done. They are called safety trolls and they are not welcome.

You obviously find a passion for telling people about safety. Please go create an instructable on safety and post it. Do not use another persons great project as a forum to get your opinion heard. This author deserves thanks for their work, encouragement and where appropriate, constructive criticisms on the technical aspects of their instructable.

Safety troll post are not welcome and forcing the author to defend his own safety practices is discouraging and just plain rude. Please be more considerate in the future.

comb joints: There are better and much safer ways of making these. The question to ask before you start modifying anything or making a jig is... is this best,safest and simplest way of doing this. If the answers are 'no' or 'not sure' then it isn't safe so don't do it if you valve you fingers, eyes and anything else you rely on to do practical tasks.

It is called a Table Saw "Sled" not "sledge!
Nice job though!
I like your saw. Nice work there...
As far as the safety police adding their 2 cents down there, They will always find a way to chime in. I have found it easiest to just politely thank them and move on...
Be safe!

Why the need to make your pyrimids from Solid Material i.e Wood…? Why not use flat material like a Veneer thts maybe a 1/8"/3/16th" in thickness and make your jigs accordingly so you can cut all the angles necessary on a flat plain vs. using your jigs with all the fancy (IMO unecessary)not to mantion more dangerous up in the air angles on TS ?

Using a Veneer then simple gluing all 4 sides togeather with a light sanding afterwards would yield a much better & IMO more accurate pyramid….. Good luck !

I really appreciate your sharing this!
...Mindmapper1, I appreciate and respect what you are saying, however some tools are and always will be inherently dangerous by nature of what they do.
I am a forty year old tradesman who has come to realize that the most likely source of injury in operating any tool is a complacent operator.
Please, ALWAYS wear safety glasses! That being said, some procedures require a table saw to have the blade guard removed. When using it, step up and be careful, alert and anticipate problems before they can happen.

Very nice job, a pleasure seeing a professional at work. one quick question I have going nuts looking for a table saw like your, do you plan to make an instructable on how to make one? I've been trying to get my hands on a plan for years now. Great job.