Using a RAS safely

[Sawdust]

Rather than drag the SCMS thread off topic, I'm opening a new one because I beginning to think I have been using my RAS the wrong way ever since I bought it about 15 years ago.

I always leave the blade at rest behind the fence (i.e. closest to the wall), place the timber to be cut against the fence and then cut on the pull, i.e. guide the saw slowly backwards to make the cut.

I do appreciate what people are saying about the tendendy of the blade to bit and dig in, although this is definitely much improved with a negative rake blade.

Have I really been using my machine the wrong way all this time?

thanks for any help
Mike

 

[Andy Pullen]

I think a fair answer is that this is how people tend to use them because it is the easiest way but on a light machine it isnt a particularly safe way, the safest way being to draw out the blade then cut towards the fence. It takes more time and effort to do this though and that is why people do it the other way. IMO.
One other point, if you were cutting a housing how could you maintain a consistent depth with the saw head climbing erratically whereas if you fed in it would be consistent with no effort.

 

[mailee]

With the RAS the idea is to pull gently on the blade and not rush the cut. Most of them come with some form of pull back spring making it easier to cut with as this fights against the climb. I too use mine as you describe and as long as I don't pull too hard it works well. I have had a couple of RAS's and still cut housings with them as I have done for many years now without any problem. I think it would be difficult to line up the cut with a pencil mark with the saw in front of the timber as your view would be obscured by the motor and blade IMHO. :wink:

 

[Scrit]

Andy

What I'd say is don't take up teaching wood machining! Please see my reply to this topic here

Lest anyone accuses me of industrial machine bias I've owned a DW111, two DW125s and I still have a DW1751. All of these machines are "lightweight" RASs.

The relevant diagram is this one, I feel:

Scrit

 

[Andy Pullen]

So you would say that drawing a light RAS towards you is a safe way of working if you have a substantial timber to cut through ?
Jerking, blade stopping, not my idea of fun.
Maybe a compromise would be to draw out for lighter cuts and in for heavy cuts. I understand exactly what you are saying but to my mind on a light machine it just aint safe, or particularly good for the machine to be constantly jarred and jammed.

 

[Scrit]

One other point, if you were cutting a housing how could you maintain a consistent depth with the saw head climbing erratically whereas if you fed in it would be consistent with no effort.

:?: :?: :?:

If you are using a cutter from the inboard (rear) to the outboard (front) of the machine the cutting dynamics (in fact Newton's Third Law of Motion states that "All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction") dictate that the workpiece will be pressed downwards and to the rear whilst outboard to inboard would result in an upwards and rearwards reaction to the cutting action.
My experience of using RASs with dado heads leads me to conclude that using a dado head in this second way, especially a non-limiter/non-kickback stacked saw type, would be an extremely hazardous operation - not one I'd attempt too often! The upcutting motion woulkd also result in a much poorer quality of cut with the edges of the cut being spelched where the teeth have lifted them at the exit point from the timber

Scrit

 

[Andy Pullen]

One other point, if you were cutting a housing how could you maintain a consistent depth with the saw head climbing erratically whereas if you fed in it would be consistent with no effort.

:?: :?: :?:

If you are using a cutter from the inboard (rear) to the outboard (front) of the machine the cutting dynamics (in fact Newton's Third Law of Motion states that "All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction") dictate that the workpiece will be pressed downwards and to the rear whilst outboard to inboard would result in an upwards and rearwards reaction to the cutting action.
My experience of using RASs with dado heads leads me to conclude that using a dado head in this second way, especially a non-limiter/non-kickback stacked saw type, would be an extremely hazardous operation - not one I'd attempt too often! The upcutting motion woulkd also result in a much poorer quality of cut with the edges of the cut being spelched where the teeth have lifted them at the exit point from the timber

Scrit

Well you certainly wont get much consistency by back cutting with a light underpowered machine that is trying to jump over the work and similarly with your 12x2 oak example, how much fun trying to cut through that with a DW720. I can see a good argument for either way but thankyou I'll do it a way I know I can control and that I feel safe with on a light machine. Held down against a fence it isn't going anywhere. YMMV.
Andy

 

[Scrit]

So you would say that drawing a light RAS towards you is a safe way of working if you have a substantial timber to cut through ?

Yes. What I am also saying is that your approach seems downright dangerous and runs contrary to all my experience and training. I've gone so far as to produce a pair of drawings which explain why that is the case, Andy.

Jerking, blade stopping, not my idea of fun.
Maybe a compromise would be to draw out for lighter cuts and in for heavy cuts. I understand exactly what you are saying but to my mind on a light machine it just aint safe, or particularly good for the machine to be constantly jarred and jammed.

Would you agree that a DW125 is a lightweight machine? After all it has a puny 1.5HP motor (and yet I can cut 16mm wide x 8mm deep housings with mine). I have rarely experienced the problems you mention for the following reasons:

1. The set-up of the RAS needs to be checked periodically to ensure that everything is in alignment, including the table surfaces and back fence

2. I always ensure that the blades are sharp

3. I almost always use a negative or zero rake blade. Positive rake blades are designed to work on table saws and will be jerky and try to climb or lift more readily on the RAS

4. I don't try to use a blade with too many teeth for deep cuts on the RAS, a 10in blade with 40 to 48 teeth will work very well except for cutting small section pieces such as beadings.

5. I avoid trying to cut knotty or badly bowed/warped timber on the RAS (or many other places for that matter)

6. If the machine is bogging down in cut then I try either reducing the speed of cut or turning the work over or very rarely cutting in two passes. I also consider changing the blade and check that the blade and arm are both square to the back fence. It may also be worthwhile checking run-out on the blade. Mailee once had a problem where the inner blade flange was bent and I have seen bent arbors a couple of times (machines dropped in moving)

7. I never attempt to use a RAS for ripping (I did when I started using one in the 1970s). Now that can be really scary!

I've found that bogging down and cutting problems are more indicative of a poorly adjusted machine, damage or a blunt blade than anything else.

Well you certainly wont get much consistency by back cutting with a light underpowered machine that is trying to jump over the work and similarly with your 12x2 oak example, how much fun trying to cut through that with a DW720. I can see a good argument for either way but thank you I'll do it a way I know I can control and that I feel safe with on a light machine. Held down against a fence it isn't going anywhere.

A DW1751 is the long arm version of the DW1251. The DW1251 is the predecessor of the DW720 but actually has less power. I, and many others, have no problem with crosscutting on such a "small, underpowered" machine, yet you do, Andy. I'd really have to question if you've got either a set-up problem there, an incorrect/blunt blade or something is broken/bent, because my experience is the same as that of many other people. I do get consistent results cutting housings and I've used my lighter RAS with a dado head for short batch work with a more than acceptable level of consistency, so I suspect that there is something else wrong with your set-up, either that or you're a kitchen fitter....... :wink:

Scrit

 

[Jake]

The moral of the story is that Andy should be Pullen'.

 

[Sawdust]

The moral of the story is that Andy should be Pullen'.

:lol: :lol: :lol: :lol:

Very good

 

[mailee]

Jake, I think that is a hat, coat and door scenario. you are awful but I like it. :lol:

 

[DomValente]

In the fifteen years that I owned a RAS cuts were always made on the pull and cannot recall the blade'climbing'.
The only time that this occured was when trying to ripcut, not a practise I would recommend.

Dom

 

[David C]

Scrit is of course correct.

When making cuts in the traditional manner, the workpiece is pushed downwards to the table and backwards to the fence by the blade. This is much safer than most table saw cuts.

Yes there is a distinct tendency for the motor to drag itself forward into the cut. We resist this with a straight right arm, and right foot placed well back. Sharp blades, proper set up, correct blade choice and a steady feed all help to minimize this

De Walt used to sell a hydraulic damper to resist this tendency, (I think) wish I had bought one.

Forums can be a source of dangerous advice. How is the novice to distinguish safe practice from dangerous practice?

David Charlesworth

 

[Sawdust]

Thanks for the advice on this.

I started the thread because the comments I read on the SCMS thread were completely contradictory to my way of using the RAS and while I don't consider myself a novice (after using the machine for about 15 years), I am an amateur and have no formal training in machine shop safety.

I think Andy's comments about the blade digging in are vaild and having experienced it, it is pretty scary - a bit like a kickback on a table saw. I avoid it by being vary aware of the depth of cut I'm making and making a very slow and steady cut - especially in thicker material. Also, as I said before, the negative rake blades are much better in this repsect.

As long as the machine is used in this manner, I find that it cuts cleanly and I have no problem cutting or trenching. I always cut tenons with it and find they fit accurately and I don't experience the problems Andy was talking about.

Finally, my machine is definitely not a huge industrial machine. It's a Ryobi with an 8 1/4 inch blade and definitely falls in the 'light' RAS category.

As for using it the other way, i.e. cutting on the push stroke. I think there would be a tendency for it to lift the timber off the table and dig in that way and I just can't see how it would be practical to use the machine this way for cutting long planks which would have to be fed through from the side.

I completely agree with Scrit's comments about ripping on the RAS - I tried it once and it was enough for me - Never again!

Once again, many thanks
Mike

 

[lurker]

I had always thought push was safer than pull.

However having studied Scrit's drawing I now see the error of my ways.

 

[staffie]

Thanks for this post everyone, this has helped a lot. I got an older DW110 a few weeks ago and have just finished restoring and setting it up. I am going to try it out this weekend the safe way. Last week tried it the unsafe way and had a few scary moments.

Once again thanks for the help.

Jock

 

[ivan]

People push the mitre saws, presumably because the saw/motor is hinged to allow it to rise and fall vertically, unlike a RAS?

Extreme judder on the proper RAS pull cut can be caused by badly adjusted head bearings. These should be tight so you can't stop the rotation with a thumb. (mind you don't trap it and pinch it!)

 

[Lee Brubaker]

I don't mind being the dissenting voice with respect to RAS operation. I bought my RAS new in 1958. It is a American Machine & foundry DeWalt 1hp 9" blade unit(Purchased before Black & Decker got their mitts on the DeWalt tool line from AMF). I also purchased the operation & maintenance book for the saw(seperate from the manual). I still do not have a table saw. I think after almost 50 years of use that I have some inkling on how to use the saw.
Firstly, as Scrit has said, the correct way to crosscut is to pull the blade through the wood. Of course there is a tendency for the blade to "climb", however, careful slow cutting & this is a rarity. If you have access to a good blade manufacturer, one with a negative rake to the teeth will reduce this tendency even more.
I have never had a kick-back ripping lumber. It is likely because I have my saw nested between two workbenches of exactly the same height as the table on the saw preventing a long board from lifting in-board or outboard of the saw blade during the cut. ALWAYS set the anti-kickback device mounted at the rear of the saw. When ripping with an RAS or a table saw NEVER reach behind the blade to hold the work to the fence during the cut. Should a kickback occur at least with an RAS the anti-kickback device may prevent you cutting your hand off however a lot of people use their table saws without the blade guard & a kickback in the above situation can result in serious injury.
With a 9" blade ripping thick stock can be troublesome hence in my case I rip thick stock on my bandsaw.
I was given a compound miter saw on a folding portable bench when I retired. I found it no more accurate than my RAS & a darn sight noisier with a universal motor .... so it sits folded up leaning agains the shop wall.

Lee

 

[orangetlh]

PUWER regs state that a RAS should have a mechanism to return the blade back to the park position. Back cutting with this mechanism would be extremely dangerous as the cutter will be pullng itself into the timber. I have never used a RAS in this way and would consider it extremely dangerous not only for above reason but also because the blade will be completely unguarded until it enters the timber.

 

[Scrit]

I have never had a kick-back ripping lumber. It is likely because I have my saw nested between two workbenches of exactly the same height as the table on the saw preventing a long board from lifting in-board or outboard of the saw blade during the cut. ALWAYS set the anti-kickback device mounted at the rear of the saw.

Possibly, Lee, but it's probably also down to the type of timber you've been sawing. Kickback occurs when either the stressed material tries wrapping itself around the rear of the blade (the effect of which should be reduced on European-supplied RASs as they've been supplied with riving knives and anti-kickback pawls for something like 30 years) or when stressed material goes the other way as it exits the saw and this results in the material being trapped between the back fence and the blade (all too possible on a RAS). If you've only ever sawn relatively knot-free and properly dried timber I'll concede that it is possible to have never experienced a kickback. I wish I could say that I had been so luck. In my early days with a DW111 it was my only saw and attempting to rip certain hardwoods on it was at times a hair-raising experience! The point you make about supporting stock is well made. As a trade woodworker I sometimes forget that what is for me mandated and which I take for granted - an adequate run-off table - is rarely supplied with the saw and many hobby woodworkers are unaware of the need for it on grounds of safety

Scrit