Radial arm saw setup and use? (accuracy)

[julianf]

As mentioned elsewhere, i have a Dewalt DW125, like this -

(not my unit, but mine is the same)

I need a table / fence arrangement for it, but that's where it all starts getting confusing.


There seems to be an "authoritative" text on the tables, in a book called "mastering the radial arm saw" where the author advocates a table made of two sheets of wood, milled for metal inserts in the middle, in order to maintain flatness

Whenever i do any searches, the same stuff comes up.



But then i see plenty of units mounted into benches like this -

So, im confused -

Can someone who actually uses one of these let me know how perfect i need to be with the table?

Ill let you know what i was planning on doing -


Screwing a flat-ish bit of wood to the top.
Screwing or clamping a fence on.
Cutting a plank at 90, checking the angles, adjusting the fence.


Am i a total heathen who is just missing the point entirely?

 

[Wendelspanswick]

If you just use the existing frame and screw timber tables to it what happens is the tables sag over time as the ends are unsupported.
You either have to brace the tables or do as you've shown in the picture above and make a proper framed and supported table.

 

[brewdexta]

The two bits of MDF with the metal bars in is called a Mr Sawdust table after the old guy's nickname who advocated it. I bought one of his books off his widow. The guy was more used to the much older RAS made of big lumps of cast iron rather than the newer pressed steel variety but the principles the same.

I have made one and it works a treat, no sag, and the fence arrangement is flexible, all simple stuff. I have the the ELU version of the same DeWalt RAS. It takes a while to set it up properly but worth doing right. The top needs to be parallel to the saw across its whole width and depth so you need means of adjustment. I only use it for 90 degree cross cuts, either through a board or for tenons. A decent blade helps, I have tried cheapies but now use an atkinson walker blade and it is much better.

In terms of whether the Mr Sawdust table is better than the RAS being built into a bench top as per your picture, not sure it matters. I didn't want to dedicate a long piece of wall space to the RAS, if I have long timber to cut I use a roller stand for in and out feed.

I do have an old Faithful mitre saw that I have screwed to the top of a mobile stanley tool chest that I have used for most of the house renovation for oak skirtings and architrave and has worked a treat, however if I wanted to really nice precision mitre saw I would probably end up buying a festool sliding mitre saw or similar.

 

[Wendelspanswick]

Only very rarely do I move my RAS off the 90° position, if I want to cut mitres I chop to length then use an appropriately angled block on the RAS table and hold the work piece against that and cut again.
For mitres in architrave mouldings and picture frames I cut oversize on the RAS and then use a mitre guillotine to trim to size, pretty much guaranteed tight joints with no splintering.

This sort of thing.

 

[tlovatt]

It depends upon how long you want the table to be, My father has one and just used chipboard circa 20 years ago and never had a problem, you also do not need an adjustable fence, use a fixed one as the whole arm will move to set angles, then set the height to lightly score the table and cut through the fence at the standard angles, this give you a good accurate idea where the saw will cut.

Woodwork requires a lot less accuracy than metalwork.

 

[tlovatt]

Also forgot to say - beware of screwing on the fence - you will need to keep in mind that the saw runs through the fence at multiple locations and so you will need to put screws in the right place and avoid other areas - it is better to glue it on either dowelled or using biscuits.

 

[Wendelspanswick]

It depends upon how long you want the table to be, My father has one and just used chipboard circa 20 years ago and never had a problem, you also do not need an adjustable fence, use a fixed one as the whole arm will move to set angles, then set the height to lightly score the table and cut through the fence at the standard angles, this give you a good accurate idea where the saw will cut.

Woodwork requires a lot less accuracy than metalwork.

I dispute the last line. If you cut a piece of steel too short you can just fill the joint with weld and no one will notice, if you cut a stile too short on a hardwood door and try and bodge it with filler it will stand out like a sore thumb.

 

[brightspark]

tell that to a cabinet maker

 

[brewdexta]

The top on the table I have is covered by a thin sheet of sacrificial ply. The fence is clamped to the back of the table top and again is sacrificial, a bit of old PAR.

Bars in place before glue up

in place with sacrificial top, I don't have the fence in place on this pic and I have no other pics with me but a couple of lever clamps bolted to the RAS base pushes it against the back of the table. I have a few of different heights.

 

[tlovatt]

I dispute the last line. If you cut a piece of steel too short you can just fill the joint with weld and no one will notice, if you cut a stile too short on a hardwood door and try and bodge it with filler it will stand out like a sore thumb.

I am not disputing the consequences of cutting things too short, I did not say or imply that you can cut wood to any length, but as I correctly stated, woodwork requires less accuracy i.e. you work to wider tolerances than with metalwork.

 

[Wendelspanswick]

I am not disputing the consequences of cutting things too short, I did not say or imply that you can cut wood to any length, but as I correctly stated, woodwork requires less accuracy i.e. you work to wider tolerances than with metalwork.

I still disagree with you, if I'm machining a window casement I will work to +-0.5mm, if I'm fabricating a steel building then +-3mm is OK.

 

[bigegg]

The Mr sawdust table is for the 1950s original US radial saw that could be made accurate to 0.1mm and 0.1deg.
I don't think the modern stuff is as solid.
I use a 10ft length of kitchen worktop with a couple of length of unistrut under it for support.
I put a piece of 6mm MDF on top as a sacrificial top.
I find the main thing, accuracy wisr is to find ways not to alter the settings.
Cut to length, then use an angled fence to cut mitres, rather than move the arm to an angle.

I also NEVER EVER use it to rip.

 

[julianf]

This brings up another question that ive been thinking about -

A lot of people seem to leave them in the 90 degree position all the time.

Why is that?

The "clamp" on mine for the 90 degree slot is wedge shaped, so i cant see that there would ever be any play, or, indeed, if it does get ware, the ware will be equal, and it will still centre correctly.

So why are people so keen on leaving them in one position?

 

[brightspark]

I am not disputing the consequences of cutting things too short, I did not say or imply that you can cut wood to any length, but as I correctly stated, woodwork requires less accuracy i.e. you work to wider tolerances than with metalwork.

if u produce bog standard run of the mill stuff your correct but if your making half decent stuff id want it 100 percent accurate not near enough . it took a while to set my chopsaw up till the mitres and joints were perfect with a square using a quality blade and I only use it on new wood not crap

 

[bigegg]

This brings up another question that ive been thinking about -

A lot of people seem to leave them in the 90 degree position all the time.

Why is that?

The "clamp" on mine for the 90 degree slot is wedge shaped, so i cant see that there would ever be any play, or, indeed, if it does get ware, the ware will be equal, and it will still centre correctly.

So why are people so keen on leaving them in one position?

Because it's a ballache to set it up square in all the directions.

Then every time you set it back to 90 it has to be done again.

I'm not saying "don't".
I'm saying that if you can make (or buy) a mitre fence (adjustable ones can be bought) - it's much easier than adjusting the saw settings.

Saying that, there's not another machine as versatile when it comes to milling timber.
I made over a 1000m of bookcases with mine a few years ago - that was a LOT of dadoes done on one resharpening of a dado set - I dread to think how many router bits I would have used.

 

[Johnseat]

I've had a radial and sold it on because of how easy it is to have it running out with a small nudge of the arm ect...
Also all the variables of the head rotating and swivelling means it's a pig to get perfectly accurate and for it stay perfectly accurate.
If you are hoping to rip with it the don't as the saw likes to try and rotate out of 90 to the workpiece which in turn causes kick back and binding.

IMO the are ok for pulling at 90° to the work piece and that's it.

 

[the artfull-codger]

Once you've got the dw 125 set up you can move the radial arm to any position you want within it's capacity, & it goes back perfectly accurate for 90 degree cuts & 45 degree cuts as the heads located with a pin & socket so it's allways accurate.

 

[tlovatt]

That depends what you're doing...

A bit of fencing, sure, 1/16" here or there won't matter much - that said, prefab railings have more adjustment than that.

Get into proper wood bashing though and the tolerances reduce - around 0.1° out on a picture frame corner will show, 0.040" out on a cabinet door will show, etc.

I'm not exactly referring to bunging in door frames in a new build house here - I mean real carpentry.

If you are talking of 'real' carpentry you will need to compare it with 'real' metalworking, you can not compare precision woodworking to bodging something up on metalworking.

Picture frames do not need to be within 0.1 degrees - having made plenty in my time this is nonsense, the different pieces of wood will move more than that during the different seasons with humidity.

 

[WorkshopChris]

But then i see plenty of units mounted into benches like this -

My one is on a bench similar to that but the workshop floor isnt anywhere near level.( think old cow shed).
Setting the saw square is just one battle. the fence runs along the back of the bench. and i just cant keep the thing accurate.
The weight of the saw slowly twists the back of the bench, and the timber moves through the seasons as the wood moves.
It only gets used for rough cuts now, when i get a chance it will go back on a steel frame, with support table either side.

 

[julianf]

Once you've got the dw 125 set up you can move the radial arm to any position you want within it's capacity, & it goes back perfectly accurate for 90 degree cuts & 45 degree cuts as the heads located with a pin & socket so it's allways accurate.

See this is what i thought. And its not even a "pin" as in round pin, that could ware, and get slack, but a wedge that 'pins' into a slot. So ware is taken out, and the wedge will center to the same point again.

But that is in contrast to...

Because it's a ballache to set it up square in all the directions.

Then every time you set it back to 90 it has to be done again.

So im still left wondering! : )