I just learned something regarding blade tension!

[OCtoolguy]

This won't be anything new to you more experienced scrollers but for those newbies and oldies like me, this is newfound info. I had read about doing this somewhere here on SSV but had never really done it until today. I had installed a new Pegas #5 MG blade and tensioned it the same way I always do. But something was just not right after cutting for just a short bit. The blade was acting funny. So, I released the tension lever and the blade had a big arc in it as if it was too long. So, what I learned is, install the blade, tension it, run the saw for a minute or so and then retension it. I was amazed at just how much the blade had stretched. When I install a blade, I always pull down on the upper arm and then tighten the clamp screw. Then pull the tension lever to apply the actual tension. This is the first time That I have ever noticed the stretch in the blade. Amazing.

 

[Fab4]

Hi Ray:
I guess it's true what they say
Never too old to learn something...lol
Fab4

[kmmcrafts]

Ray do you suppose the blade actually stretched or do you suppose the upper arm etc wasn't completely rested to the lowest point?

I asked that because ( mind you I have the cheap China made saw.. but.. I've found that on the Excalibur and even on my old DW788 the upper arm always dropped down more after I tension  the  blade.. SO what I almost always do now is push down on the upper linkage while tightening the thumb screw..BUT that doesn't always do the trick.. so Now I just do as mentioned but once tension is on I then release it and re-clamp the blade then saw.. It's an extra step.. and kinda in some ways annoying to do.. but.. doing so has always made the blade as tight as it should be.. 

Not an issue with the Hawk.. and many times I've seen recently that folks talking about the blade stretching.. I don't think it's stretching that much.. especially when I never have the issue with the Hawk.. The Hawk has a bottom out hole for the lower clamp.. put the blade in until it rest on the bottom and tighten the thumb screw.. somewhat the same with the top provided you have it adjusted properly the blade should come up just under the stop pin in the upper clamp.. so there is no fuss with the Hawk.. each blade goes in the same way every time..and one should never need to adjust this unless they swap blades from a large number to a very small number.. Anyway.. My point is.. the blades don't stretch on the Hawk but they do on the EX? I think it's more about putting a load on the upper pivots of the upper arm.. This is the downfall to these types of saws in my opinion.. way too many pivot points and bearings sleeves etc.. But not knocking the saws.. they are awesome to cut on.. until they get some wear.. then you get a little more slop and get the blade stretching issue.. LOL If that's what you want to call it.. 

[OzarkSawdust]

Ray, I've noticed that before. Tha first time after putting a new blade in. But just didn't pay it any attention. 

I've tried to pluck the blade to see if it has a high clear tone...but my music is playing too loud on the Bose to hear it...lol

By the way...if there are some really good tunes on, and you're changing the blade to the next hole...don't start tapping your foot if you use a foot switch...….don't ask me how I know 

[Wilson142]

I watched a you tube video a bought pre-tensioning blades. Don't remember who the guy was, but he is a well known scroller. I'll look to see if he is in my subscribed list (after the Raiders game!) He would run the fresh blade awhile and then re-tension before cutting. I prefer to install the blade, make a few cuts and then re-tension. 

[Rockytime]

This subject has come up before. I'm with Kevin. My Hawk never had a problem as the blade is always positioned the same. Same with my Hegners. Foolproof clamps.

[trackman]

Mine (EX21) does the same thing. I think you are on to something about stretching. Seems odd that after putting in a new blade an cutting for a short time the tension goes away. But after this happens once it doesn’t happen again. I know what Kevin is saying but if the clamps or arms wasn’t down first time you reclamped then it should happen again with the same blade that you clamp several times before it gets worn out. As a side think (lol) I worked on railroad for 41 years and I know how much steel grows when it gets hot. Makes sense a blade getting warm cutting will expand some. 

[JimErn]

I started running a new blade for 30 sec or so back at the start when I had a porter cable, it happened on that one too.  Some blades stretch and some blades don't, but it doesn't hurt anything to do it, so I do.

[OCtoolguy]

15 hours ago, kmmcrafts said:

Ray do you suppose the blade actually stretched or do you suppose the upper arm etc wasn't completely rested to the lowest point?

I asked that because ( mind you I have the cheap China made saw.. but.. I've found that on the Excalibur and even on my old DW788 the upper arm always dropped down more after I tension  the  blade.. SO what I almost always do now is push down on the upper linkage while tightening the thumb screw..BUT that doesn't always do the trick.. so Now I just do as mentioned but once tension is on I then release it and re-clamp the blade then saw.. It's an extra step.. and kinda in some ways annoying to do.. but.. doing so has always made the blade as tight as it should be.. 

Not an issue with the Hawk.. and many times I've seen recently that folks talking about the blade stretching.. I don't think it's stretching that much.. especially when I never have the issue with the Hawk.. The Hawk has a bottom out hole for the lower clamp.. put the blade in until it rest on the bottom and tighten the thumb screw.. somewhat the same with the top provided you have it adjusted properly the blade should come up just under the stop pin in the upper clamp.. so there is no fuss with the Hawk.. each blade goes in the same way every time..and one should never need to adjust this unless they swap blades from a large number to a very small number.. Anyway.. My point is.. the blades don't stretch on the Hawk but they do on the EX? I think it's more about putting a load on the upper pivots of the upper arm.. This is the downfall to these types of saws in my opinion.. way too many pivot points and bearings sleeves etc.. But not knocking the saws.. they are awesome to cut on.. until they get some wear.. then you get a little more slop and get the blade stretching issue.. LOL If that's what you want to call it.. 

Kevin, it only seems to happen when changing blades. I know what you are talking about so I always try to take the "slop" out of the linkage before tightening the clamp screw.

 

[Scrappile]

I have not notice this yet on my Hegner or Seyco..  Maybe on the Hegner it is because I have to adjust the tension often.  I think my tension mechanism is wearing out. 

Edited November 8, 2019 by Scrappile

[Jim McDonald]

I have noticed this from time to time.  Can't say if it is a particular lot of blades because I dump the new ones in on what was left in the storage tube.  So, in theory, I could have some 5 year old blades still in the tube and just haven't gotten to them yet.

[Gonzo]

On November 7, 2019 at 6:06 PM, octoolguy said:

This won't be anything new to you more experienced scrollers but for those newbies and oldies like me, this is newfound info. I had read about doing this somewhere here on SSV but had never really done it until today. I had installed a new Pegas #5 MG blade and tensioned it the same way I always do. But something was just not right after cutting for just a short bit. The blade was acting funny. So, I released the tension lever and the blade had a big arc in it as if it was too long. So, what I learned is, install the blade, tension it, run the saw for a minute or so and then retension it. I was amazed at just how much the blade had stretched. When I install a blade, I always pull down on the upper arm and then tighten the clamp screw. Then pull the tension lever to apply the actual tension. This is the first time That I have ever noticed the stretch in the blade. Amazing.

 

The exact same thing happens to me, and I do the exactly as you do. I figured it was just one of the nuances of scrolling. 

[John B]

I must confess, I do the same,Run the machine for a a little while when replacing blades then re-tension it.
Both Ex and the DeWalt

[Wilson142]

On 11/7/2019 at 5:27 PM, kmmcrafts said:

Ray do you suppose the blade actually stretched or do you suppose the upper arm etc wasn't completely rested to the lowest point?

I asked that because ( mind you I have the cheap China made saw.. but.. I've found that on the Excalibur and even on my old DW788 the upper arm always dropped down more after I tension  the  blade.. SO what I almost always do now is push down on the upper linkage while tightening the thumb screw..BUT that doesn't always do the trick.. so Now I just do as mentioned but once tension is on I then release it and re-clamp the blade then saw.. It's an extra step.. and kinda in some ways annoying to do.. but.. doing so has always made the blade as tight as it should be.. 

Not an issue with the Hawk.. and many times I've seen recently that folks talking about the blade stretching.. I don't think it's stretching that much.. especially when I never have the issue with the Hawk.. The Hawk has a bottom out hole for the lower clamp.. put the blade in until it rest on the bottom and tighten the thumb screw.. somewhat the same with the top provided you have it adjusted properly the blade should come up just under the stop pin in the upper clamp.. so there is no fuss with the Hawk.. each blade goes in the same way every time..and one should never need to adjust this unless they swap blades from a large number to a very small number.. Anyway.. My point is.. the blades don't stretch on the Hawk but they do on the EX? I think it's more about putting a load on the upper pivots of the upper arm.. This is the downfall to these types of saws in my opinion.. way too many pivot points and bearings sleeves etc.. But not knocking the saws.. they are awesome to cut on.. until they get some wear.. then you get a little more slop and get the blade stretching issue.. LOL If that's what you want to call it.. 

DW788 is the only saw I have and I notice some stretch in new blades. Occasionally I'll start a project with a new blade, find I have to re tension and than decide that's not the blade I want for the piece. In those cases I remove the nearly new blade and place it in a tube to use later. I don't seem to have a tensioning problem with those when I come back to them. 

[Sycamore67]

This is an interesting topic and maybe someone has measured a blade before and after use.

I took some #3 FD Polar blades and compared the length new and they were all exactly the same as viewed thru a magnifying lamp.  These blades have a thickness of 0.010 to 0.011".  I took a blade and mounted it in my Hegner saw and tensioned it as hard as I thought reasonable and more than I would normally do.  The blade had a very high pitch sound when plucked.  

I then ran the saw at full speed for about 10 minutes and was cutting 1/2" ash.

I took the blade out and compared the length to that of several of the new ones and could not detect any difference.  With the blade clamps, there is no bending or such where it goes into the clamp.  Maybe there is some elastic stretching that happens which goes back to normal when taking it out of the clamp.  I could not find any permanent plastic deformation of the blade that I used.  Others may find something different but it would certainly be interesting for others to measure or compare their blades before and after use.  Maybe other saws put more strain on the blades.  

It is unfortunate that one can not easily measure blade stretching with a blade in the saw.  I have done this  on my band saw to measure the tension on the blade.  I am going to continue to think about  a way of measuring the deformation of a scroll saw blade.  

It would really be nice to know the exact grade of steel and heat treating that the blades go thru when being made.  The best I could find is a high carbon steel which is heat treated using an oil bath for quenching.  

[amazingkevin]

On 11/7/2019 at 7:50 PM, OzarkSawdust said:

Ray, I've noticed that before. Tha first time after putting a new blade in. But just didn't pay it any attention. 

I've tried to pluck the blade to see if it has a high clear tone...but my music is playing too loud on the Bose to hear it...lol

By the way...if there are some really good tunes on, and you're changing the blade to the next hole...don't start tapping your foot if you use a foot switch...….don't ask me how I know 

That,s too funny!!!

[JimErn]

@Sycamore67

My understanding of the manufacturing process is that it all starts as a roll of high tensile steel wire.  That is fed through a press to flatten it, then a punch to get the teeth, and finally a cutter.

Blade stretch is going to be hard to measure.  I think is going to be like the Concorde airplane, it is designed to "grow" 6 inches due to the high speed friction, but it returns to normal specs very quickly - I would imagine that would be true of the blade too, heat and it stretches and before you can measure the heat dissipates and it returns to normal.

[kmmcrafts]

I honestly don't believe it is stretching like you all claim.. Find it hard to believe that they stretch for the Ex type saws but not the Hawks and Hegners.. Seems fishy to me.. I still believe it is something to do with the saw design itself.. Again.. not picking on any type of saw in particular.. but I experience this same thing on my EX.. but not on my Hawk.. What gives? different type of saw mechanisms.. 

I've never really had a blade run hot on the Ex types of saws to the point that they discolor but have on the Hawks.. yet I still had no issues with loosing tension.. so this really makes me believe it's not a blade issue..

[Sycamore67]

The question remains about retensioning.  If the blade returns to the original length as Jim suggests, then you would not need to re-tension.

The coefficient of thermal expansion is 0.0000072.  So you would multiply the blade length by the temperature (C)increase times the coefficient to get the expansion.  Even if the blade temperature reaches 500 F. The expansion of a 5" blade is only about 0.018" .

I think that in some conditions of you are pushing your wood hard you could deform the blade.  Or a bit of blade slip in the clamp could cause issues.  I just have not been able to measure or see any increase in blade length.  I am hoping that others will try to measure.

No matter if it is stretch or clamp slipoage, losing blade tension is an issue.

The skin temperatures of the SST were not too extreme compared to the SR72 Blackbird.  It leaked fuel until the plane got hit enough to expand and seal the tanks

[OCtoolguy]

Now you guys have me thinking and what you say does make sense. I'm wondering if there might just be a tiny bit of slippage in the clamps that allows the blade to "bow" a bit when the tension is removed. I'm going to have to really watch and see if that is the case. I have been cleaning the ends of the blades because I have noticed that my newest batch seemed to have more oil on them. I haven't tried sanding or roughing the ends but it may come to that. I know some here do that as a general rule. I've never done it but it may just be that the Pegas clamp screws are just too shiny/slick to hold the blades firmly.

 

Edited November 10, 2019 by octoolguy

[JimErn]

I sand the blade ends, use to need to do it before I got the pegas clamps so it is a habit, not sure if I still need to but it has become part of the ritual so to speak.. 

Whether it is clamp slippage or stretch, I do not know, but once I run the blade for 30 sec or so, it does not happen the rest of the time I use the blade.  It is not like I put in the blade, tension it, and cut and done, I do a lot of fretwork so it is cut, release, tension, cut, etc

[amazingkevin]

On 11/7/2019 at 7:27 PM, kmmcrafts said:

Ray do you suppose the blade actually stretched or do you suppose the upper arm etc wasn't completely rested to the lowest point?

I asked that because ( mind you I have the cheap China made saw.. but.. I've found that on the Excalibur and even on my old DW788 the upper arm always dropped down more after I tension  the  blade.. SO what I almost always do now is push down on the upper linkage while tightening the thumb screw..BUT that doesn't always do the trick.. so Now I just do as mentioned but once tension is on I then release it and re-clamp the blade then saw.. It's an extra step.. and kinda in some ways annoying to do.. but.. doing so has always made the blade as tight as it should be.. 

Not an issue with the Hawk.. and many times I've seen recently that folks talking about the blade stretching.. I don't think it's stretching that much.. especially when I never have the issue with the Hawk.. The Hawk has a bottom out hole for the lower clamp.. put the blade in until it rest on the bottom and tighten the thumb screw.. somewhat the same with the top provided you have it adjusted properly the blade should come up just under the stop pin in the upper clamp.. so there is no fuss with the Hawk.. each blade goes in the same way every time..and one should never need to adjust this unless they swap blades from a large number to a very small number.. Anyway.. My point is.. the blades don't stretch on the Hawk but they do on the EX? I think it's more about putting a load on the upper pivots of the upper arm.. This is the downfall to these types of saws in my opinion.. way too many pivot points and bearings sleeves etc.. But not knocking the saws.. they are awesome to cut on.. until they get some wear.. then you get a little more slop and get the blade stretching issue.. LOL If that's what you want to call it.. 

Your exactly right!!!

[Sycamore67]

Several possibilities that could cause loss of tension. Probably good to check tension after you saw for a few minutes on a new blade.

[ike]

I agree the blade does not stretch. I do a lot of fretwork and sometines it appears that the bllade stretches, but if you set your tension and release it

and it sems like it stretches  if you if you see some stretching tak it out and dheck the leght. it wiill be the same I tried it and checked the lght. with a set of electronic calipers and there was no differench. the blade doesn't stretch  at times i believe the blade slips a little. I use Olson blade so I can't speak obout other blades depends on the material the blade is made of.

IKE

 

Edited November 14, 2019 by ike

[Woodrush]

On 11/7/2019 at 7:50 PM, OzarkSawdust said:

Ray, I've noticed that before. Tha first time after putting a new blade in. But just didn't pay it any attention. 

I've tried to pluck the blade to see if it has a high clear tone...but my music is playing too loud on the Bose to hear it...lol

By the way...if there are some really good tunes on, and you're changing the blade to the next hole...don't start tapping your foot if you use a foot switch...….don't ask me how I know 

that is the only draw back with a foot switch.just saying for a friend