Thread: Saw Blades

Radial arm saws are not designed for clean cuts - the position of the blade relative to the work does not allow for a chip free cut.

Your best option is to try a blade with a triple-chip tooth profile or a hollow face profile (triple chip is MUCH easier to find and is cheaper as well) with at least 72 teeth (the more teeth the better - I think you can get up to 108 in a 400mm blade), but no guarantees that this will get rid of the router.

Can you explain this? I have a SCMS, which is a RAS AFAIC. What about this saw makes it bad for coated surfaces, or is there a difference

As far as I can see, the scriber blade was invented for a reason, whatever the platform.

I am not being a BAD GUY. I am just wondering if your writing off the RAS includes the SCMS (and probably the TS) and what is the true solution as you see it.

I'll try to answer as best as I can with the aid of my professional Paint drawings

Without getting too technical (and I don't profess to having the knowledge to get technical), it comes down to the actual geometry of the blade and how the teeth contact the wood. In a RAS/SCMS (yes they are essentially the same) the blade spins in the same direction as the "feed" (or the way the timber would feed if the fence didn't stop it) and only projects a few mm on the other face of the board. With a table saw the blade projects above the work and spins AGAINST the feed direction.

The blades for laminates are designed to project about 15-25mm above the surface of the board to allow the teeth to contact at the proper angle.

The scriber WAS invented to cut the bottom of the panel a fraction wider than the main blade (about 0.1mm) so that when the teeth push the chips down, they won't take bits out of the underside.

While I'm saying that RAS-type saws are not for laminates, I am absolutely NOT writing off the table saw. It is the best way to cleanly cut laminates aside from a CNC router and, while the scriber is better, selecting the proper blade will result in a cut nearly if not just as good as having a scribe.

After all, the machine is merely a tool holder and the tool will determine the quality of finish. A $1,500 table saw, properly tuned for square and alignment, with the right blade will outperform a $50k panel saw with the wrong blade every time.

Hope that somewhat disjointed assortment of words sheds a bit of light on the issue.

Elan

Thanks for that. Apart from feed direction I can see the angle with which the teeth hit the plastic would be important.

However I am puzzled about the feed direction. If you turn your table saw picture upside down, isn't the feed direction the same in relation to the blade's travel through the wood the same in both cases. You describe the feed as being the way the wood would go, in the RAS, but as far as the blade is concerned, the "feed of the wood" (if there was any) is out away from the fence and into the blade

So blade geometry/protrusion matter, but the feed is the same.???

no, feed is not the same. in a RAS the blade spins in the same direction as it travels through the wood, in a TS the blade spins against the feed

Originally Posted by sprog1

Hi, can anyone adivise me what is the best blade to use on a radial arm saw. I cut mainly partical board, faced with melimine, & no matter how fine the blade is, the melimine still chips, so that I have to router to get a good finish. Are there any blades I can use, that will cut smooth, so I don't need to router. Thanks

I do have to ask one question. Are you doing enough of this that using the router to finish is a real problem? I say this because I cam to discover that "saving time" can be a trap, if you are looking at only a small portion of the process. By this I mean planning, buying, marking, cutting, finishing, joining/gluing....something like having to use a router can be annoying, but be careful about obsessing over it.

AH! OK. Checked out a video. So a RAS is NOT as much like an SCMS (which is what I have) as I thought. I can't believe that you are supposed to accept the saw's push, rather than push against it, on a RAS. It seems wrong. AFAIK all planes, saws etc have you push against the flow rather than accept it as on a RAS.

Originally Posted by REALOldNick

AH! OK. Checked out a video. So a RAS is NOT as much like an SCMS (which is what I have) as I thought. I can't believe that you are supposed to accept the saw's push, rather than push against it, on a RAS. It seems wrong. AFAIK all planes, saws etc have you push against the flow rather than accept it as on a RAS.

I would like to see the source of the video. You should definitely NOT allow the saw to do its own thing EVER. In sheet material it's not so much of a problem, but solid timber will bite and jam the blade - been there and done that many times.

I would like to thank Nick, & Elanjacobs for the information I have recieved. I would like to buy a panel saw with scriber, but I can't afford a panel saw & also, the one's that I have seen have all been to heavy for my workshop, as i'm on the 2nd floor. It looks like I will have to look for a new blade, & carry on useing the router.
Yes Nick, I am using sheet materal all the time, & if I could get a good finish with just a saw, it would save a lot of time.
If I made a decent size panel saw, & a cross cut saw, similar to the Triton, & I used good blades, would I still get the same problems, do you think? Ron

Regardless of the saw used, chipping of laminates/coated boards is caused when the saw tooth completes its cut and exits the material and can break out a chunk of coating.

With a basic table saw, chipout would occur on the lower surface as the tooth leaves the work and passes back under the table surface. Using a sacrificial zero clearance insert on the table and setting the blade protrusion carefully should ensure that there is proper support for the material /coating at the point where the tooth leaves the material.

With a radial arm saw, the cutting action is to position the work against the fence, start the saw and draw the saw from the rest position near the pillar, through a gap in the fence toward the user. To make a through (full depth) cut, the blade height is set to cut about 1mm into the table surface, which is rapidly degraded. However while it is in good condition, the surface acts as a zero clearance support and protects the lower material surface from chipping. However, after a few cuts with minor tracking errors caused by the multitude of saw setup adjustments, the kerf in the table surface starts to become wider and degrades the support available to the lower surface of the work. The upper surface is generally safe because the saw tooth is entering the work, and the the material bulk supports the coating.

With a SCMS, the system appears similar to a radial arm saw, except that there is a plastic insert with a wide gap instead of a table. However, as I understand it (I don't use one) the action is different in that the work is positioned against the fence, the saw is drawn out beyond the work, the saw is started, plunged down so the blade enters the slot in the insert, and then is feed back toward the rest position to make the cut and finally stopped in the rest position. In this motion, the tooth leaves the work at the top of the material and it is not possible to provide any support to avoid chipout on the surface.

As previously mentioned, a panel saw uses a small scribing blade before the main blade to cut a shallow trench in the lower surface of the material and coating. This blade rotates in the oposite direction to the main blade so the bulk of the material supports the surface as the tooth enters the work preventing chipping. The trench is marginally wider than the kerf of the main blade and aligned with it, so as the main blade completes the cut from the top, there is a small clearance between it and the scribed trench walls, so the main blade does not cause chipping of the lower surface.

The above assumes a perfect arbour and blade, but arbour runout and blade flex become involved and can produce minor chipping of the unprotected face of the material as teeth pass through the established kerf prior to making their next cut. Panel saws typically have 32mm arbours whereas recreational table saws, RAS and SCMS have arbours in the range 16mm to 20mm. The larger arbour has a cross section area and rigidity about 3 - 4 times that of the smaller unit.

Sprog, I could send you construction articles for a couple of wall mounted vertical panel saws if you are interested. These are based on a circular saw but can support a full sheet of material and make horizontal and vertical cuts. With adaption of the basepate to allow for replaceable zero clearance baseplates, and a total weight of about 80 Kg, these may solve your problem. Have been planing on building one for a few years but haven't got around toit yet.

Hi Malb, thanks for the advice, I think i've got all that.
You must be a mind reader, i've just been discussing Vertical Panel Saws today with a friend of mine. Yes I would like as much information as poss on how to make one, whether I could get the parts out here though, is an other matter.
I don't suppose you have any informatiom on how to build a overhead router, have you? I saw a artical in the routing forum a couple of days ago, & forgot to save it, now I can't find it. Thanks

Malb
I reckon some sort of zero clearance setup could be done for an SCMS, but it would probably be cumbersome and inconvenient.

sprog1 I reckon building a panel saw is a job in itself. I would take it on as a project for its own sake, if there was no alternative. You are talking of saving time..... Also I do not reckon a triton-style setup is going to give you what you want: the heavier the unit, given equal quality, the better the job. Sheet metal is IMO OK for field work, but not finer work on large sheets.

BTW, what blades have you tried? It's not just about tooth count. There are blades designed to cut "melamine".

I actually think that a vertical panel saw makes a lot of sense, especially for a careful home build (but still consider time) and in a smaller shop. It is also easier to load a large sheet vertical or near vertical onto a foot plate than flat onto a table saw. LIke Malb I have given it some thought and it's in the back of my mind. I would stress that unless you get a very good saw you may be disappointed. The base you make for the saw will overcome a lot of the lacks of a sheet metal saw base, and you can align the blade properly, but IMO unless you get a good saw you will not come up to the accuracy of a decent table saw.

I know routing takes up time, but I stress _compared to the overall project_?....but then, while I want to make things of wood, I have bought tools just for the heck of it uurrgh uurrgh

Thanks Nick, getting anything out here is hard, & where I live next to impossible, it's either something light for DIY & won't last 5mins or it's industrial & expensive.
Unless it's a factory, most Thai's make their own saw benches out of ply with a circler saw placed upside down, so there is not much call for anything in between.
Saw blades, i've only been able to get normal carbide tipped blades with 100 teeth, there must be somewhere to get ones to cut melamine, but as yet i've not found anywhere. I know I can get one off the internet, but getting things through customs is hit & miss, if I want anything like that I have to wait until a friend comes to bring it out for me, you people don't know how lucky you are, when it comes to getting tools. It looks like I will end up useing the router, at least I do get a good finish. Thanks again

Hi again, one thing I forgot to ask, which blade would you recomend.
I have just been looking at the CMT blades at Carba-Tec they have a melamine & fine cut off or a melamine & chipboard, which would you rercomend.
The reason I chose Carba-Tec is, I have a friend coming next month, who works near to them, in Brisbane.