dickross Posted December 7, 2015 Report Share Posted December 7, 2015 I have a Dewalt 788 saw. When looking at the blade motion. The blade goes down and back away from the operator. Then up and forward. This seems backwards!!! and the forward and back motion is around .090". This seems excessive.. If I was going to design a saw from scratch I would try for .040 or .050" front to back motion (2 X tooth height on avg. blade) and the blade would move forward on the down stroke.. Are all scroll saws made this way? What am I missing? Dewalt is a big company, surely they must have a couple people smarter than me! Just for grins, I put a blade in backwards and tried pulling the wood into the blade. It seemed to cut faster and was very much easier to hold down. It was very hard to follow a line. I'm sure that is partly due to just being a new way to do things. Dick Quote Link to comment Share on other sites More sharing options...
wbr Posted December 7, 2015 Report Share Posted December 7, 2015 I think this video addresses that amazingkevin 1 Quote Link to comment Share on other sites More sharing options...
LarryEA Posted December 7, 2015 Report Share Posted December 7, 2015 linkage geometry Why? Just Because! Quote Link to comment Share on other sites More sharing options...
jerry1939 Posted December 8, 2015 Report Share Posted December 8, 2015 I have a Delta that was purchased new this summer. It's identical to the 788. Interesting video. My old $70 Menards did not have the noticeable front to back motion and was better for cutting corners. Have quit sawing for the winter, but will try a different approach in the spring. The blades seat further back in the blade clamps than is necessary. Will cut a very narrow strip out of heavy "tin", such as the side of a coffee can. Place it in the bottom clamp and bend it around the clamp to hold it in place, propping the bottom of the blade forward. Don't know if I will succeed or fail. If you place bets, keep them under $5 dollars please. Don't want you going hungry. jerry amazingkevin 1 Quote Link to comment Share on other sites More sharing options...
amazingkevin Posted December 8, 2015 Report Share Posted December 8, 2015 I think this video addresses that wbr thanks for the flick,it's one I don't have! :thumbs: :thumbs: :thumbs: Quote Link to comment Share on other sites More sharing options...
JohnR48 Posted December 8, 2015 Report Share Posted December 8, 2015 I followed that video 3 months ago and the results are most significant. Work in stages, as a little bit goes a long way. Well worth the effort. Quote Link to comment Share on other sites More sharing options...
dickross Posted December 10, 2015 Author Report Share Posted December 10, 2015 I made that modification a couple years ago shortly after I got the saw.. It did help a lot but doesn't address the the question I asked.. Both arms that hold the blade are 4" long from pivot point to blade. The stroke is .75". If you do the math that means the blade moves back and forward .071" as it strokes up and down. The arms are horizontal when the blade is raised to the top of the stroke. that means the blade is moving back, away from the operator, as it goes down.. If you run the saw at its slowest speed and look at the blade at eye level. you can almost see that its going down and back at the same time. Or, stop the saw with the blade at its highest point. Then place a scrap of wood against the back of the blade, push the upper arm down manually. You'll see the blade kick the wood back about a 1/16". I'd really like to hear from somebody with another brand saw to see if it's made the same way. Dick Quote Link to comment Share on other sites More sharing options...
LarryEA Posted December 10, 2015 Report Share Posted December 10, 2015 I have two Delta's. A 40-690 and a 40-694. Both my saws have that slight movement of the blade back and forth. I do not notice any problem when I saw. This movement does not affect my fret cutting in any way at all. Suprisingly, if you ignore it, it's a problem that will go away. Joe W. 1 Quote Link to comment Share on other sites More sharing options...
dickross Posted December 10, 2015 Author Report Share Posted December 10, 2015 I've spent my whole life making things better or finding new ways to do things. It's just not in me to ignore something that looks wrong. Sometimes it turns out I'm the one that's wrong, Sometimes I get another Patent. But I generally end up a little smarter than when I asked the question. Dick Quote Link to comment Share on other sites More sharing options...
dickross Posted December 10, 2015 Author Report Share Posted December 10, 2015 LarryEA, I forgot to ask, On your Delta saws. Does the blade move forward or backwards on the down stroke?? Dick Quote Link to comment Share on other sites More sharing options...
jrpeteo Posted December 10, 2015 Report Share Posted December 10, 2015 I did modification shown in the video except I slotted the holes in the back by the pivot rather than the ones by the linkages. I also raised the back of the table by using a customized pivot thingy. The combination helped immensely. Pete customized pivot thingy, wood one was a prototype. Quote Link to comment Share on other sites More sharing options...
LarryEA Posted December 11, 2015 Report Share Posted December 11, 2015 LarryEA, I forgot to ask, On your Delta saws. Does the blade move forward or backwards on the down stroke?? Dick On the down stroke, moves forward at the table level about 1/32" Quote Link to comment Share on other sites More sharing options...
tomsteve Posted December 11, 2015 Report Share Posted December 11, 2015 i have an ex 16 and it has that action. the blade pulling away just a little is enough for the dust to fall from the cut.quite often im cutting 3/4". not all teeth leave thecut on the stroke. so with the blade pulling back justa wee bit allows fresh cut dust to leave the gullets. if the gullets cant get the fresh cut dust out of the way the blades heat up, blades dull quicker,cuts can get wavy...there are a few other problems that can happen. LarryEA 1 Quote Link to comment Share on other sites More sharing options...
LarryEA Posted December 11, 2015 Report Share Posted December 11, 2015 i have an ex 16 and it has that action. the blade pulling away just a little is enough for the dust to fall from the cut.quite often im cutting 3/4". not all teeth leave thecut on the stroke. so with the blade pulling back justa wee bit allows fresh cut dust to leave the gullets. if the gullets cant get the fresh cut dust out of the way the blades heat up, blades dull quicker,cuts can get wavy...there are a few other problems that can happen. I like this explaination. I didn't think every Delta and Dewalt were manufactured with that 'defect'. Quote Link to comment Share on other sites More sharing options...
Dan Posted December 12, 2015 Report Share Posted December 12, 2015 I have a Delta P-20. I just checked the blade movement as I do every time this type of question comes up. My blade moves forward about 0.031" on the down stroke. This seems normal to me. Quote Link to comment Share on other sites More sharing options...
dickross Posted December 13, 2015 Author Report Share Posted December 13, 2015 Moving forward on the downstroke would seem like the logical way to design the linkage. For some reason, Dewalt reversed this on the 788. The stoke is .75" so when cutting .75" wood the chips should clear regardless of forward or back motion. Also does anybody know the difference between the 788 type one and the 788 type two?? Quote Link to comment Share on other sites More sharing options...
redwine Posted December 13, 2015 Report Share Posted December 13, 2015 This is the nature of the beast and not being a mathematic expert by an means, it seems that 2 arms that are connected together and move up and down on a solid mounting point will produce that back and forward movement of the blade. Now the only scroll saw that I know of that the blade absolutely moves up and down square to the table, is the Eclipse made here in the US, but you will shell out about $1700 or more for it. This scroll saw uses some type of belt and mechanisement to produce the straight up and down movement of the blade. Google the site and details about the working can be found. Redwine tomsteve 1 Quote Link to comment Share on other sites More sharing options...
Jim Finn Posted December 21, 2015 Report Share Posted December 21, 2015 I have two Hegners and one very old Jet and they all have no forward and back motion that I can see. (Their moving arms are 15" -25" long) So in answer to your question , yes, there are $aws that do not have this problem. Quote Link to comment Share on other sites More sharing options...
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