NVR on SCMS?

[OPJ]

Hi guys,

I know I'm not the only one who using a sliding compound mitre saw for cross-cutting. I'm not a great fan of radial arm saws but, one advantage they have that I like is that you can 'lock' the saw on. With a mitre saw, you have to release the trigger each time you stop and, when you've got a batch of repeat-cutting to do, it feels rather tedious and almost unproductive (to me, anyway).

What I'm wondering is what it would be a good idea to connect one of these saws to an NVR box? So that, with the trigger locked off (cable tie or similar), the saw could continue running continuously.

Do you think this is a good idea? Is there any reason (motor, etc.) a saw like this should not be used in this way?

Obviously, there is a H&S element to consider and the head of the saw would have to be raised correctly after each cut.

Thanks,

Olly.

 

[Eric The Viking]

Do you think this is a good idea? Is there any reason (motor, etc.) a saw like this should not be used in this way?

Obviously, there is a H&S element to consider and the head of the saw would have to be raised correctly after each cut.

Duty cycle of the motor may be a consideration - how long it's on for compared to being off. I'd have thought actually it's a bit better for the motor to have it continually running, as the fan is cooling it without it being under load - depends on design.

(later, after Googling: Perhaps not-so-good: many of these (all of them?) are commutated http://en.wikipedia.org/wiki/Universal_motor#Universal_motors, and there is specific mention in the link of such motors potentially being damaged by no-load running for significant periods. So it would wear out quicker.

That said, there's no real reason not to temporarily have an NVR switch in-line. If you wanted to experiment, you might try the old router trick of a cable tie round the trigger (and an NVR switch borrowed from the router, assuming the power handling is within limits).

The thing I'd worry about operationally was where my hands were and where the blade and blade guard were, in other words where you put it. The old Wadkin starters were either up on the arm itself, or on the edge of the bench in front. You don't want to be reaching to the back!

Speaking as a leftie, I generally find trigger-locks are a confounded nuisance, to the extent I've on occasion stripped the switch and removed them (on the lawnmower, for example). SCMS arrangements are annoying because they're invariably for right-handed people! If an NVR switch helps leftie ergonomics, it's got to be a good thing!

 

[Mattty]

I think you would be crazy to do this Ollie. It would be extremely dangerous in my opinion- and for what? A possible few seconds saved over the course of a day?
I cant think of an scms that i have used that isn't ready to cut within well under a second of the trigger being pulled.

 

[RogerS]

Ollie - Go into the bathroom and hold up your hands to the mirror. Count your fingers. Ten? Good. Keep 'em. You are crazy to even consider doing this. :wink:

 

[Racers]

Hi,

Just tried that I got 20 in total (10 in the mirror and 10 on my hands), so I can afford to lose 10. :wink:

Pete

It is crazy to by-pass the switch!

 

[Mcluma]

get one with a good electronic brake and its not a problem

there is no need for an NVR switch - to dangerous

 

[Mike.C]

Olly mate it's not worth it.

Cheers

Mike

 

[Eric The Viking]

I'm not trying to start a huge argument, but what _exactly_ is more dangerous about using an NVR switch, compared to a trigger?

I'm making the assumption that the blade has the usual retractable guard that returns immediately it's lifted from the workpiece, and that the NVR switch is in a safe and sensible place, for example at the front of the bench, and that the point is to do repetitive cutting, where you won't be setting the blade every time, either because it isn't critical or because you have a stop.

I don't use SCMSs a lot (I don't own one, but have borrowed them and serviced them too), so this isn't a troll but a genuine question. There have been several 'you're crazy' responses, but no explanation.

I'm happy to be called ignorant (I'll learn!), but please, someone explain why...

 

[OPJ]

As Eric says - if you guys could please clarify exactly why you think this is so dangerous then, I'd be grateful.

I wouldn't use this for cutting long lengths or sawn timber, where the saw blade is probably most likely to bind or snatch. In such a situation, the trigger switch is ideal because you simply let go and it stops (or, runs down).

There may be an issue of 'breakout' on the upper face but, with a sharp blade and the correct number of teeth, I doubt it would be much of a problem, if any.

I'd only be cutting prepared boards to repeat lengths. I wouldn't use it for mitring or bevel cuts.

Again, as Eric says; the guard retracts automatically and I know where and where not to put my hands.

This is just a thought at present. I have no intention to order an NVR switch and get going ASAP. Some further explanation would be appreciated, though...

 

[RogerS]

....
Again, as Eric says; the guard retracts automatically and I know where and where not to put my hands.
.....

That's what I thought, as well. My cover retracts. I was adjusting the position of the stock to make a trim cut. The blade was still rotating. The cover had not fully closed.

Using the saw is ingrained in us...squeeze trigger, saw works. So if we aren't squeezing then the blade can't be going round, can it?

 

[Lons]

Hi,

Just tried that I got 20 in total (10 in the mirror and 10 on my hands), so I can afford to lose 10. :wink:

Pete

It is crazy to by-pass the switch!

:lol: :lol: :lol:

Just relate that to the song "ten green bottles" and start counting down!

 

[Chems]

I can't see how it is any more dangerous than a RAS to be honest, like Olly says the SCMS has a guard that comes in the RAS doesn't. Of course just like the RAS it does increase the chance of you somehow lowering an active blade on your fingers.

 

[Benchwayze]

(Seen on a true-life Hospital programme)

A guy in Brum managed to sever his arm just below the elbow, and he was using an SCMS just as it was issued. Even he couldn't say how his arm got dragged in, but it did.

So OP, the first thing I thought was the same as Matty... Don't go there.


John

 

[RogerS]

Your fingers - your call.

 

[devonwoody]

I often look at the plastic guards on my machines and think to myself, if I crashed into that blade guard the blade would cut through just like butter, so I think blade guards are more of a warning guard than real protection in some accident circumstances.

 

[Eric The Viking]

I often look at the plastic guards on my machines and think to myself, if I crashed into that blade guard the blade would cut through just like butter, so I think blade guards are more of a warning guard than real protection in some accident circumstances.

That makes good sense to me.

One reason I like the old Elu/DeWalt SCMS is the metal guard. It has a tendency to 'tire' with age (the return spring's groove gets bunged up, mostly), but it's really solid.

Let's make a list:

#1 (against): Blade guards aren't that solid, so the less the saw is running, the safer everything is overall. Rank: 6/10

#2 (against): Continual running of the motor under no-load conditions may damage it. Rank: 2/10

#1 (for): Having the saw switched separately is one less thing to worry about (paraphrase of Olly). Rank 4/10.

#2 (for): As a lefty (with duff hands), I'd be concentrating more on the cut if I wasn't fiddling with the mechanical interlock on the trigger. Rank: 3/10

So I think the anti- argument is winning at the moment (average 4/10, versus 3.5/10).

If this isn't a good way to do it, please say so (we could have a poll once we've collected enough arguments, and people could rank the statements they agree with).

 

[RogerS]

Back to the OP...

when you've got a batch of repeat-cutting to do, it feels rather tedious

This to me implies wanting to save time and boredom. These two reasons are the cause of many an accident. So you're rushing to finish the job, you reach in, the blades still going round.....bye-bye digits or hand.

The blade guard will have gone down so that won't happen. Not on my DW707 it won't. As Eric said, it gets sticky with sawdust and so slow to release.

BUT WORST OF ALL....when you clamp up the trigger, the blade guard retracts by 50% leaving a large part of the blade unprotected.

So you're rushing to finish the job. How do you clear away all the pieces that you've cut off as they are going to back up. Reach in and ...oops.

Why not go the whole hog. Why bother with an NVR? What's wrong with a 13A socket and plug it straight in?

 

[jhwbigley]

I can't see how it is any more dangerous than a RAS to be honest, like Olly says the SCMS has a guard that comes in the RAS doesn't. Of course just like the RAS it does increase the chance of you somehow lowering an active blade on your fingers.

I feel that the Radial arm saw is a lot safer than a chop saw, its why i only ever use my chopy when i'm awa from the 'shop.

A radial arm saw should be fitted with a spring return, which pulls its back to its parked position behind the fence , where it is no halm to anyone.

also the bigger the ras the better 8)

JH

 

[OPJ]

Another reason I thought of all this is because I'm quite paranoid (among many other things.... :roll about how much electricity I consume... Each time I start the saw up (Makita LS1013 with a soft-start brush motor), I notice the lights dim. If I'm batch cutting for, say, twenty-minutes then, that's a lot of extra electricity, given that the starting current of any electrical tool is often greater than the running current (or something like that).

With planers, thicknessers, table saws and bandsaws, we don't have to stop-start so often. Though, I agree in part that the design of your average SCMS is only suited to site use and not for continual use in a busy workshop.

With regards to clearing the waste, I have an MDF false fence fitted permanently, which not only reduces breakout, but also prevents 'bits' from gathering behind the fence. Anything else that falls to the right-hand side of the blade can be pushed clear of the 'danger zone' using the trimmed component (once the blade has retracted!) and then cleared away safely.

The advantage of a decent NVR switch is that you can easily cut the power should something go wrong. Try doing that with a 13amp socket... :? Somewhere around knee-height would probably be ideal.

Interesting Timbers have a truly terrifying saw for cross-cutting though. It clearly isn't braked though, that was the least of my concerns on my last visit there... It's an old Wadkin and I've since struggled to find a picture of it online. I guess it's regarded as a "pullover" rather than a radial arm. In fact, there is no arm; it operates on almost a "pendulum action"... Anyway.

Basically, there's no spring mechanism to guide the saw blade back in to its resting place. Instead, they wedge a block of wood (!!!) between the body of the saw and rear side of the fence! Otherwise, it'll creep out and try to get you, as my lump of 3in beech discovered (at the very least, they do switch off after each cut) :shock:

So, erm, sliding mitre saws aren't that bad, at least....