I just bought a nice and shiny Elu SCMS and it says on the machine to only use blades with negative rake
Why?
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I just bought a nice and shiny Elu SCMS and it says on the machine to only use blades with negative rake
Why?
Funky,
The operation of a most SCMS's is to push the saw across the work. With a negative rake blade you lower the saw through the work then pull it towards you.
Ian
So it doesn't matter if I'm using a blade with positive rake then? As long as I'm pushing it into the workQuote:
Originally Posted by Ian Smith
Quote:
Originally Posted by funkychicken
I believe it is because negative rake blades have less of a tendency to draw the material into the blade and hence when pushing the SCMS through the material (and it really should always be pushed through, not pulled) the material is less likely to draw back into the blade and away from the support fence.
Dado blades often have negative rake too for this same reason, so the material is not drawn into the blade as easily and hence offers more control over the workpiece for the user.
I hope I didnt get that backwards :p
Funky,
As I understand it
Negative rake is more suitable for use in mitre saws because it tries to push the timber into the saw fence
Positive rake blades are used in hand-held circular saws as these blades try to lift the timber into the saws base plate.
I have a Trade Tools SCMS and it has a negative rake blade - does a very nice cut too - and the bloke there was at pains to point out to pull rather than push the saw through the work. It is quite noticeable during operation that the saw is driving the work against the fence and is almost self propelled when doing a wide cut.
So to answer your question, yes, as far as I am aware you can fit a positive rake blade to your SCMS but you should push rather than pull it through the work
I am not aware of any design feature which would restrict the use of either type of blade in an SCMS. However, it would not seem wise to fit a negative rake blade to a hand-held circular saw
Ian
positive rake means that the edge is in front of the rest of the blade as it strikes the work material. So the edge hits the material and the waste goes down the blade at an angle of less than 90º.
This is good when cutting stuff like Steel or Stainless or Wood mostly. Things like Brass which is soft but brittle you need negative rake where the edge hits the material but the waste is forced back at an angle greater than 90º.
Positive rake can drag the tool into the work, so with soft material like wood negative rake might be advantageous, certainly were you only want to cut to to a depth such as you do with a dado blade verses cutting right through as you typically are doing with a regular blade. For a SCMS negative rake has it's advantages.
There is a big difference between rake and clearance. On a circular saw blade you will see clearance angles on the front and sides to that the edge is not fouled in it's attempt to cut the material. Rake deals with the part where the waste material is removed.
Studley
In the case of that particular saw it reduces the agressiveness of the blade and allows you to climb cut with control, the way the saw was designed to be used. You can cut by pulling the body to the end of the slides and cutting with a push stroke, but as you may have found with that particular saw design, it is not so easy unless the saw is clamped or bolted down and at about hip height.
Cheers
Michael
Hi Funky,
since i already had a discussion about this with other tool users in another forum, i can reuse the tips and pics i used then. There was a mix-up then about rake, since with saw teeth the story is exact the opposite as with vehicles. Streamlined wedgeshape fronts (slanted back as it were) are raked positive and when negatively raked, the top parts sticks out more. I gathered some pics of locomotives to illustrate my point back then.
Positively raked saw teeth have their top parts sticking out in sawing direction, at an angle between 5 and 15 degrees measured against radials towards the blade's arbor. The higher the angle, the more the teeth are tended to eat into the wood. Positive rake teeth are meant for handheld circular saws and saw tables and are great for rip cuts, because the teeth tend to pull the wood towards them, which makes for great speed and effect.
With a mitre saw, there already is more than enough pressure from above to sink the saw blade into the wood. Furthermore, the spinning direction and the teeth friction are more than enough to secure the wood against the machine. That means that with positive rake teeth, the blade would fret into the wood at a ludicrous pace and almost immediately stall the motor. Besides, any careful adjustment of pressure and cutting progress would be impossible. Therefore, mitre saw blades have zero rake or slightly negative rake. Negative rake is espcecially advised when the saw is induction motor powered. The torque characteristics of an induction motor are such that it is most efficient up to a maximum of 20% rpm loss, after that the torque collapses quickly and the motor stalls. This is especially the case with single phase motors; three phase motors have more pulling power and recovery reserves at reduced rpm. Three phase motors also startup better in under-load conditions, single phase motors do not perform that great, unless fitted with additional current consuming measures like extra startup condensers, and are therefore better started up with no load.
Below, you also find some worthwhile saw blade links as found on the web. Especially the "justsawblades"-one is instructive.
Cheers from Holland!
gerhard
http://www.plasticsmag.com/features....sue=Mar/Apr-01
http://www.wacatools.com/tctsawblade..._knowledge.htm
http://www.summitsawblades.co.uk/product_range.htm
http://www.starrett.co.uk/support/Te...l_Information/
http://justsawblades.com/systimatic/terminology.htm
Hi
Oh no, :oo: not the negative vs positive rake blades again :doh:
Much of what you read on this subject both here and other forums to put it politely is rubbish.
There are uses and needs for both kinds of blade. I have been through this neg vs pos rake several times now. I can confirm that either will work well in the correct circumstances. In *ALL* circumstances the material being cut should be clamped so the "lift" of the blade realistically can be ignored.
The requirement for Elu SCMS to only use blades with negative rake is most likely also the same kind of misleading information. Unless there is some specific design feature that SPECIFICALLY NEEDS a neg rake blade, which I seriously doubt, then either blade pos or neg can be used.
In ALL cases safety should ALWAYS be paramount in your mind when using ANY machinery - with a negative hook blade OR a positive hook blade.
Much of what you read can also be misleading, who should you believe? Why should you believe me? All I can tell you from my point of view is that as a Radial Arm Saw (RAS) owner (the superb "forerunner" to the SCMS) for more than 30 years I have had real world experience of both the RAS AND the SCMS with both kinds of blade.
There ARE legitimate needs for both types but your decisions should not be made on silly reasons.
The direction of cutting action on an SCMS is to PUSH the blade through the material, NOT pull it through. The action is the OPPOSITE on a RAS. Having vast experience on BOTH tools I can say that the push action on the SCMS and the PULL action on the RAS IS correct!
Rubbish! the direction remains the same.Quote:
The operation of a most SCMS's is to push the saw across the work. With a negative rake blade you lower the saw through the work then pull it towards you.
Correct.Quote:
So it doesn't matter if I'm using a blade with positive rake then? As long as I'm pushing it into the work
There is no real difference pos or neg blades push the timber toward the fence.Quote:
Negative rake is more suitable for use in mitre saws because it tries to push the timber into the saw fence
Just as they try to push the timber into the fence on an SCMS.Quote:
Positive rake blades are used in hand-held circular saws as these blades try to lift the timber into the saws base plate.
I disagree and think the bloke there is not too competent with tools.Quote:
I have a Trade Tools SCMS and it has a negative rake blade - does a very nice cut too - and the bloke there was at pains to point out to pull rather than push the saw through the work.
This...
• During a slide cut, gently push the carriage toward
the guide fence without stopping. If the carriage
movement is stopped during the cut, a mark will be
left in the workpiece and the precision of the cut will
be impaired.
...is from the Makita SCMS user manual here ...
http://www.manualnguide.com/dl/10056/
or this...
MAKE SLIDING CUTS by pushing the saw blade down
on top of the workpiece then sliding it back toward the
rear of the saw. DO NOT pull the saw toward you while
making a cut.
...from here
http://oneworld1.inetu.net/manuals/r...Z1_964_eng.pdf
or this...
9. During slide cutting, always push the saw blade away from the operator.
...from here
http://www.hitachipowertools.com/pro.../C10FSH_OM.pdf
I think you get my point :wink:
A negative hook blade can be used in a hand held circular saw to help prevent chip out on the TOP surface of the material being cut.Quote:
However, it would not seem wise to fit a negative rake blade to a hand-held circular saw
You should NEVER use a positive hook blade when cutting metal on an SCMS!Quote:
This is good when cutting stuff like Steel or Stainless or Wood mostly. Things like Brass which is soft but brittle you need negative rake where the edge hits the material but the waste is forced back at an angle greater than 90º.
Cutting plastic and aluminium on an SCMS is a valid use of a negative hook blade.
WHAT? :? If that WAS the case then there would be no need for anti kick back pawls :doh:Quote:
Positive rake teeth are meant for handheld circular saws and saw tables and are great for rip cuts, because the teeth tend to pull the wood towards them, which makes for great speed and effect.
What?Quote:
That means that with positive rake teeth, the blade would fret into the wood at a ludicrous pace and almost immediately stall the motor.
What?Quote:
Besides, any careful adjustment of pressure and cutting progress would be impossible.
What? Like most table saws?Quote:
Therefore, mitre saw blades have zero rake or slightly negative rake. Negative rake is espcecially advised when the saw is induction motor powered.
Some of the answers here are not really thought through and will only serve to confuse those less experienced and seeking advice.
Here is a sample of several youtube SCMS videos...
[ame="http://www.youtube.com/watch?v=oda3RZBGoVk&feature=related"]YouTube - How to Use a Miter Saw : Basic Techniques for Making Cuts with a Miter Saw : How to Cut Crown Molding on an Outside Corner with a Miter Saw[/ame]
...and here is a great example of a properly aligned RAS with a pos hook blade doing the kind of cut you would find hard to believe :2tsup:
Here is his description of the video...
Un-edited test video using my restored 1956 10" DeWalt GW-I using a Forrest "Mr Sawdust" blade, now the WW-1 Triple Chip Grind/TCG blade. My hands are off the full 1 by 6 Cherry and I'm pulling the motor through the cut holding only the very top of the anti-kickback rod with my left hand fingertips. Blade climb and kickback are not existent. DO NOT try this at home unless your DeWalt or other make Radial Arm Saw is set up precisely and you are using a Forrest Woodworker-1 TCG for the radial arm saw. Check out my website...mrsawdust.com
[ame="http://www.youtube.com/watch?v=aUnZpUDvzgs"]YouTube - Crosscutting on a vintage DeWalt radial arm saw[/ame]
Please don't let my message or those of others stop you from asking for advice. It is worth asking if you are unsure :2tsup:
HTH :)
Mr Fixit, I RESENT the implication of your post that MY information is RUBBISH.Quote:
Originally Posted by MrFixIt
This saw does indeed have a design feature requiring a negative rake blade. It is a ps174 that used to belong to me and as I said, the information I provided is specifically related to THAT saw.
The saw has a placard on it with big red letters that the saw is to only be used with a negative rake blade. The instruction manual specifically says "activate the saw and cut down into the wood, if necessary, pull the saw head towards you (for wide timber). Start the saw with the saw closeest to the fence, plunge down into the work and draw it across the work without interruption"
The saw is not a typical scms, the slides and the saw head pivot as one. It is possible to do a push cut with it, but it requires you to first pull the saw head UP the angled slides and then pivot it down into the work. You stand corrected.
All the saws you are talking about have fixed horizontal slides and should be used as you say. The fellow with the Trade tools saw is the same principle as the Elu design and therefore the sales guy was correct in pointing out to use only a negative rake.
Cheers
Michael
OH NO!! - not another long winded post full of quotes, unnecessary bolding and capitilisation from the man who has been everywhere and done everything
Let it go mic-d - it's a slippery slope
Ian
I agree totally with MrFixit.
I have used RAS and SCMS a lot
Pull a RAS through the timber
Extend a SCMS and drop the blade and push the saw through the timber.
Otherwise you are courting disaster.
Negative rake blades have a lower tendency to climb through the timber, hence are far safer.
You know for most of the stuff that people do at home, positive or negative is not that much of an issue. My own thoughts for woodwork get a blade with that is anywhere from almost neutral to positive, BUT don't go crazy on the angle massive rake won't be good.
When you have a lot of positive rake the tool can pull itself into the job. Negative rake can do the opposite, but for cutting timber you really only need to be sensible about your choice. After all you will use the one blade for basically everything. It is not like you are machining different steels where you need positive rake and then machining brass where you need negative rake. Even as I say that I am thinking that Sandvik amongst others have done some very freaky things with their carbide tools so I think they make a tip for brass with positive rake!
just be sensible in choosing a blade and you will be fine. One thing I would recommend is not going to savage on any angle, for instance they make ATB blades for Melamine that have a really pointy tip wouldn't recommend that blade for anything else.
Studley
I use a negative rake blade on my makita scms, when I am cutting Aluminium, but find a positive rake blade gives me an easier and better cut . I have if fact 4 diffrent blades for the saw and change them to suit the material I am cutting. For me its what gives me the best results :2tsup:
I think most of you are missing the point here. The question is not a general one concerning the pros and cons of negative rake blades, it is specifically whether this saw requires a negative rake blade, as all the documentation from the manufacturer appears to indicate.
That seems to settle the matter as far as I can see. So where's the problem? Unless you're saying that funkychicken should just disregard what the manufacturer of the saw says and listen to you blokes instead.Quote:
The saw has a placard on it with big red letters that the saw is to only be used with a negative rake blade. The instruction manual specifically says "activate the saw and cut down into the wood, if necessary, pull the saw head towards you (for wide timber). Start the saw with the saw closest to the fence, plunge down into the work and draw it across the work without interruption"