Blade Travel DeWalt788

[Terry Murphy]

I have a Craftsman 18" saw, and if I am not careful when installing blades I can have significant movement. If I align my blade with the front of the clamp, top and bottom, I have minimal movement. If I push the blades all the way in, I can have a lot of movement and cutting problems.
Just my experience, and 2cents.
Its making it difficult to choose which saw to upgrade to.

[Doug Nelson]

Terry, sort of fun to watch these threads about blade movement. I purchased an Excalibur 16" and have so little forward movement it is difficult to see. I also had a Craftsman which I just looked at for fun to look at the blade movement, it is about 3/32 of an inch, probably why my arms always jerked up and down. Ask an Excalibur user if they recommend the Ex, then make a decision. Just my opinion.

[Plaquerd]

Most of you are familiar with my work. What saw do I use? The Dewalt 788, Type 1, two of them to be exact. I've NEVER had a problem with excessive blade movement, when cutting fretwork, puzzles, compound, beveled segmentation, inlay or "sculpted inlay", 99% of it with flat blades.
The quality problems with the saw are well known, but it seems to me that part of the excessive blade movement problem might be the way the blade is being put into the clamps. I put the top in first and make sure it is seated all the way into the clamp, if it is not lined up in the same configuration on the bottom clamp there is something wrong. The blade should align by itself into the bottom clamp, "straight up and down" without having to be pushed, pulled or manipulated in any way. Just my two cents.

[wedo]

For those of you interested here is a formula for calculating how much back and forth movement you should theoretically have in your scroll saw arms. The movement in math terms is called a sagitta of an arc. If you measure the distance from the pivot point of your arm to the point attaching your blade and the blade stroke this formula will calculate it. For my 21" Sakura the distance from the upper arm pivot point to the blade is 15.5" and the stroke is 1". For the formula you plug in the 15.5" as the r and take one half of the stroke as 0.5" as the L and it calculates the depth of the chord (sagitta) as 0.008". Since that is the top arm only the bottom arm also will move that much so the total should be twice that or 0.0016" That would be the best this saw could do with perfect alignment. If you want to calculate yours here is the web site Calculating the Sagitta of an Arc
Bill

[hotshot]

Wedo, these calculations don't work on the 788 or EX saws as they use a double parallel-link arm design. One of our form members that does marquetry was able to get his EX down to .035" (the manufacturer told him it could do .020"). 1/32 of an inch is .031".

I understand that different saws may be better at certain projects or styles, thats a given. However, there is still an "expectation" that the 788 will perform within certain tollerances. These saws have served many folks well over the years. A lot of great work has been created on these machines.

So, that said, if a new 788 owner wants to know if his saw cuts within the tollerances allowed by that design, what would that target for blade travel be? For the EX, I would say the answer would be around .035".

-------Randy

[Tenfingers 2]

Randy,
Using the Strut assembly and the blade chuck as the radius. I measure about 3.8" to the appoximate middle of the blade. (Measurements are off somwhat due to them not being in the same plane and it's getting late so I eyeballed it some) Anyhow using the formula It seems to me the theoretical best for the 788 would be 0.019 However after many hours of working with my 788 Type 1 0.04 is about the the best I've been able to get it to do.

I set up my saw with an Olsen #5 spiral blade clamping a straight edge to the table front to back and cut 1.5 inch maple, .75 oak, and .125 BB Ply All gave 0.35 kerf.

I then clamped the straight edge side to side and the results were,
1.5 Maple .051 top .074 bottom
.75 Oak .045 top .061 bottom
.125 BB .08

I've measured the front to back blade travel on my saw at 0.04. Can it do better or am I just wasting my time?

Maybe it's not the saw, Maybe it's the operator.

[JimSawyer]

Not for nothing, but I got my 788, (type 1), in July of '98. Like Dave, (Plaquerd), I've had no problems with blade travel, (or what is known on jig saws as orbit). Most of you have seen the work I do, and if I had significant blade travel, it wouldn't be possible....
I wonder if quality isn't the same since it's not being made by the same manufacturer....

...Just thinkin'.........

(Still love my 788.)

[mowerman1193]

Ok, I must own up to my guessing on my 788 blade travel from my previous post. Yesterday I put a #3 Ultra Reverse blade in and put a credit card on the back side of the blade. My previous guess was 1/8+ but it is actually only just slightly over 1/16. It seems like a lot compared to my two Delta saws. My Dremel 1800 is about the same as the Dewalt. I think later today I am going to check my other saws and see what I come up with. I wont be able to check my one Delta SS350 as I have it apart but I will test the others..



Thanks,
Kevin

[Rolf]

This is a very interesting discussion and I have contributed my bit, but in the overall scheme of things, if we are able to cut the projects we like to our satisfaction with a minimum of aggravation, then It all doesn't really matter.
But it does give justification to go and buy a better saw if we must.

[hotshot]

Rolf, your right, if the saw does well with the work of its' user, it serves it's purpose well. But when someone goes to purchase a saw, in order to make that determination, there has to be a set expectation for that purchase.

If it were possible for you to purchase another new G4, but upon receiving it you find it has 1/16 or even 1/8 blade travel for reasons you couldn't determine, then that saw would not meet your expectations nor be able to do the work you do, despite it's reputation. You have a certain expectation for that saw and the tollerances afforded by that design. You have a firm expectation for that saw and purchased based on that expectation.

So, what is the expectation for the 788? For those on the extreme side of this issue (those that are closer to 1/8 than 1/16), there is a whole boatload of projects that would give them issue. In evaluating the various options, should the feasbility of the 788 be based on a 1/16" movement? or perhaps Less?

What we don't know (but are getting closer to determining), is the condition of the current crop of saws are coming off the line. The last 5 folks with very recent purchases that agreed to measure this for me, measured 1/16" or less travel. If that is in line with the older Type 1s, then I would say a new purchaser has a decent chance of getting a saw that performs consistent with it's original design.

------Randy