skunkriv Posted January 25, 2008 Share Posted January 25, 2008 Think of how tall your "nut" would be to even get two full turns. The load on this one thread would be massive. The thread would crush or gall, depending on how good of steel was used and heat treatment. Flypresses are just one of those things you gotta save up for. Buy new or be prepared to jump on a good deal on a used one when it comes by. Quote Link to comment Share on other sites More sharing options...
matt87 Posted January 25, 2008 Share Posted January 25, 2008 This DIY fly pres idea may be more or less dead for many good reasons already mentioned, but I just had an idea of how to make the 4-lead screw. Take an appropriate length of, say, 2" square . Put it in the gasser for a nice even heat, clamp end in the (securely mounted) vise and twist. The square shape probably wouldn't give you the best thread cross-section, but I suppose you could swage into something better first. Not sure on how to make the internal thread. Perhaps tacking 4 lengths of stock that mates with the male thread, heating, wrapping, and then offering it up to the body of the receiving part. Tack weld the wrapped threads to receiver at the other end and grind off the tacks holding the threads onto the male thread, and remove the male thread. Put the receiver in the forge and braze. Quote Link to comment Share on other sites More sharing options...
FrogPondForge Posted January 25, 2008 Share Posted January 25, 2008 Could gearing be used to reduce the number of turns at the flywheel, using more common 4-5 turns-per-inch threaded rod/nuts? The overall torque should even out. I could see a big toothed belt drive, with a heavy spring-tensioner on the tension side. This would give the over-center release effect. (like the springs in a power hammer). There are belts, gears, chains, etc., that can transmit hundreds of horsepower. Just a thought. (FrogPond'sDad) Quote Link to comment Share on other sites More sharing options...
habu68 Posted January 25, 2008 Share Posted January 25, 2008 700 years of engineering have designed an elegant, powerful machine with one moving part that takes 20 to 30 ft/lbs of human effort and produces many tons of momentary effort and returns the unused portion of that effort to the return stroke. The two, three. or four start screws and nuts are machinable in most automotive machine shops. The frame must be massive to take the strain, The trick is the knowledge to turn the screw and calculate the strength of the frame that you are able to fabricate. Get any edition of Machinery's Handbook for about 10-20$ us on ebay to work out the math. What we are trying to do here is re-invent the wheel(fly) and the inclined plane(screw), most of that engineering was done by Galileo some time ago. Habu now dismounts his high horse.:rolleyes: Quote Link to comment Share on other sites More sharing options...
nonjic Posted January 26, 2008 Share Posted January 26, 2008 they are a very elegant machine, that, IMHO cant be improved on ( I build presses and hammers for a living) - they are also cheap for what they are, even cheap at $1000, youll get your money back if you even choose to sell. (so, effectivley they just cost the shipping, and the cost of the capital (yup, im an accounts boy originally). I doubt you could ever 'fabricate' a functional screw for one of these, a chains only as strong as its weakest link etc... some things like power hammers & hydraulic presses can be made for 'home / small shop' use better../... more cost effective than the commercial products, but im afraid flypresses cant. ! Quote Link to comment Share on other sites More sharing options...
R Funk Posted January 26, 2008 Share Posted January 26, 2008 The reason you need a mutliple start screw is so that it will not stick on the bottom. If a single start screw is used the relatively low angle of the thread on the screw is such that it is self locking. That is increased force will not cause the nut to spin off. This is what is desired for most screws and nuts. However in flypress application this will require the fly wheel/ screw assembly needs to be manually backed off. This could require a fair amount of force and time, heating the tooling and cooling the work. However using a multiple start screw the angle of the screw is such that screw/nut assembly is not self locking and will back off automatically when the assembly hits the bottom of the stroke. By the way I have (4) 2.5" dia acme thread screws with nuts I bought to make one or more flypresses. I bought these before I recognized the issue with single start screws. I guess I can use them to make a 10" 250 lb leg vice with a 2.5" screw. Of course I would sell them to a believer who thinks they will work in a flypress. Quote Link to comment Share on other sites More sharing options...
brian Posted January 28, 2008 Author Share Posted January 28, 2008 they are a very elegant machine, that, IMHO cant be improved on ( I build presses and hammers for a living) - they are also cheap for what they are, even cheap at $1000, youll get your money back if you even choose to sell. (so, effectivley they just cost the shipping, and the cost of the capital (yup, im an accounts boy originally). I think you're right John, the time I spend making one (which probably won't work) would be better spent earning money to buy the real thing. It's been good watching this idea being kicked around on the forum and the old brain cells being stretched to the limit,plus the interesting input from various people with a wide knowledge of the subject. Makes you realize how skilled those people must have been a couple of centuries ago to turn a thread like that with the machinery they had. Quote Link to comment Share on other sites More sharing options...
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