Understanding Radial Arm Saws:
Their Safe Usage & Tuning.
Today, the Sliding Compound Mitre-saw, in its various guises, seems to have overtaken the Radial Arm Saw in popularity. This may be due to the clearly, more portable nature of the SCMS; its affordability or fears over the safety of the RAS. Perhaps a combination of all three factors is at play. Certainly, many compound mitre saws are reasonably priced and can be easily stowed in the boot of the car or in the tool box of a truck. Set-up on the job is reduced to minutes.
A DeWALT 721 Radial Arm Saw
In regard to fears over safety, I would argue that all saws are dangerous in careless hands. Personally, I am much more intimidated by a SCMS or chop saw than I am by the radial arm saw. With the former, the hands (and even the body) always seem to be much too close to a ferociously rotating blade for my liking. With a proper set-up, work can be safely done on the RAS at a remove of some distance from the blade. See my blog of 9.3.2016 on the waneyedgeworkshop.com.
There is little doubt that the RAS is the most versatile saw around, with the capability of cutting dadoes, mitres, compound mitres, bevels, rabbets, half-laps, tenons and much more. Of course it is also ideal for cross-cutting and ripping when safely set up. With the appropriate jigs, one can straighten boards, joint boards and even cut tapers. I have developed a handy jig for cutting circles on the Radial Arm and Ed Waggoner Sr. has posted two videos on Youtube that even show how to cut accurate box joints on the RAS using a dead simple jig and set-up that he had developed. Moreover, the RAS has greater reach than most SCMSs. It is also possible to mount a router on the RAS to create an overhead routing system and to mount sanding heads, moulding heads etc. But for this article, let’s stick with sawing work. So, versatile the RAS is. Like most good things in life however, there is a trade-off for this versatility; a number of trade-offs actually.
First is the aforementioned price; radial arms saws tend to be relatively expensive (unless you are lucky enough to pick up a second-hand one). Second comes the portability issue; it has to be admitted that the RAS is probably better as a stationery workshop saw rather than a site saw. I wouldn’t dream of bringing mine to a site. Thirdly, there is the little matter of tuning and adjusting the RAS. If the RAS isn’t adjusted and tuned properly the quality of the cuts will be less than optimum. Yes, the radial arm saw does require a little tweaking now and then. If you only require it for cross-cutting 2x4s to length, then there is no problem; a slightly less than optimum cut probably won’t bother you that much. However, if you are interested in joinery work the RAS must be kept in tune. Indeed, it would seem a pity to own a marvellous tool like the RAS and only use it for rough cross-cutting.
Despite the trade-offs, those of us who take the time to get to know our radial arm saws, grow to love them. I mean, really love them; we wouldn’t be without one in the shop. There’s something about the RAS that is addictive. I always say that the RAS is like an olive. You know that exceedingly bitter and nasty tasting fruit that comes from the Mediterranean; on your first taste you are so revolted that you spit and cough like hell. But over time you watch your wife and her friends joyfully eating olives with Nachos while watching TV; seeming to relish in their flavour. There must be something you are missing! Curiosity makes you venture again and over time you too develop a taste for them. One day, you discover that you are addicted and would eat them straight from the jar. I think many peoples’ first experience of a radial arm saw is something like that. Their very inexperience makes them dive into some ripping operation without sufficient thought and preparation. The result is a frightening bang and a hunk of lumber shooting past their ear and out the garage door, almost killing the neighbour’s cat. At this stage, most people walk away, believing all the intrepid radial arm saw’s bad press. A few endeavour to persevere; learn from their mistakes and learn to master a really versatile and pleasurable machine. There is no doubt, a well-tuned RAS is a pleasure to use.
Before we look into the tuning-up of a radial arm saw, it is worth thinking for a moment about the difference between it and the sliding compound mitre saw. In some respects they are similar. Both have a blade that rotates in the same direction. Each has an arm of sorts. In both cases the work-piece is held against a back-fence. Yet, with the RAS we cut on the pull stroke; with the SCMS we cut on the push stroke (more correctly, we plunge and push). One is essentially pull, while the other is essentially push. Why is this?
With the blade rotating in the direction that it does, pulling the saw into the work creates a climbing cut. The blade wants to climb up and over the work. The potential for something nasty happening here is obvious. In the case of the RAS, this tendency (to climb) is resisted somewhat by the fact that the arm of the saw does not tilt up but is held rigidly at right angles to the column. Provided the work is firmly held in place against the fence (ideally clamped) all will be well.
If one were to attempt to pull a SCMS into the work, there would be nothing mechanical to prevent the saw tilting up and climbing onto the work. It would be a battle between the operator and the saw to control the cut. More often than not, the saw would win. Therefore, manufacturers of SCMSs recommend cutting on the push.
Looking at it from another perspective, cutting on the push just isn’t practical for the RAS. Because the arm cannot tilt, setting up for a push cut would be laborious, awkward and unsafe. The operator would have to pull the saw out along the arm and lock the travel. Then he would have to place his work-piece against the fence behind the saw, start up the saw, unlock the travel again and make the cut. All the while of course, ensuring the work-piece is held firmly against the fence. There is an inherent danger here of operators not turning the saw off between cuts and reaching behind the spinning blade into the cutting area to set up for the next cut. Very, very dangerous indeed. Even if the motor is off, if the operator’s hand is behind the saw and the carriage lock slipped, the non-rotating blade moving forward under the weight of the motor and yoke, onto the hand would give a nasty cut. So, fiddling about behind the blade is just not on.
But what about that climbing business; is there still not a tendency for this to give trouble with the RAS? Well, yes there is! But there is something else we do to mitigate this trouble. We fit a negative rake angle blade (or negative hook angle blade) on the RAS. This lessens the tendency to climb as the negative hook blade is less likely to grab the wood (negative hook angle blades are also recommended for SCMSs by the way).
Note the dramatic difference between the stance of each tooth. The vertical line represents the neutral position.
Without getting too deep into the geometry of saw teeth and rake angles, suffice to say that the hook angle or rake angle are terms used to describe the direction of a saw blade’s teeth (relative to the rotation and central axis of the saw blade). The higher the hook angle (i.e. the more positive or forward the hook), the more aggressively the saw blade will cut, with a greater tendency for the blade to self-feed and grab the wood or pull the operator’s hand into the saw. A neutral or negative hook angle provides more opportunity to better control the cut as the blade is much less likely to grab the wood. The diagram above shows the dramatic difference between the positive hook tooth and the negative hook tooth. Check what sort of blade is on your new saw (be it RAS or SCMS). The chances are it will be a positive rake blade; change it immediately.
Negative hook blades are usually recommended for situations where the blade is moved into the wood, push or pull, such as in the SCMS or the RAS. Where the blade is stationary, as in a table saw, and the wood is moved into the blade, positive hook blades are more often recommended, particularly for ripping. Negative hook blades in a table saw can actually cause a kick-back during rip work.
Tuning a Radial Arm Saw.
A 4-step Approach.
This is my simple, 4-step approach to tuning the RAS, which I do periodically but especially before I start an important project. It only takes about half an hour. It is important that the checks and adjustments are done in the order shown. A Radial Arm Saw can go out of adjustment due to its own vibration so re-tuning is required from time to time.
- The Table; ensure it is flat and level.
Flatness and levelness are two different things. That is why I am taking these two points together (there’s logic in that statement somewhere!). Firstly, the table surface must be flat or planer and secondly, that plane must be parallel to the plane of the arm of the saw. See the difference? Note the particular meaning we have for ‘level’ here.
A long straight edge will check if the table surface is flat. If it is not flat, take whatever steps are necessary to ensure that it becomes flat; even replacing the table surface with a new one if the existing one is chewed up and gone beyond it.
Making the table level (not level to the floor but parallel to the plane of the arm) is a different matter altogether. On radial arm saws there is usually no adjustment for the arm, so it is the table that has to be adjusted to be level relative to the arm.
To do this, it is usually necessary to plug out the saw and remove the blade guard and blade. Tilt the arbour downwards towards the table and lock in that position. Use a wooden block and a feeler gauge to test the table against the end of the arbour at all four corners of the table and in the centre. If there are differences in the gap between the wooden block and the arbour you will have to make adjustments to the table by loosening the brackets underneath the table, adjusting and re-tightening. This is a ‘hands and knees’ job, I am afraid.
I have seen people do this job without removing the blade guard and blade and using a (marked) reference tooth on the blade with the block and feeler gauge. However, I feel that using the arbour is more accurate.
- Square the blade to the table.
It is fairly obvious that to get a square cut, the blade must be square to the table. There is actually a bit more to it than this as we shall see shortly but the first step in ensuring a square cut is to square the blade to the table. To check this you will need to plug out the machine and remove the blade guard. Pull the saw out from the home position to the middle of the table where you can get at it and lock the carriage. Tighten the bevel lock with the blade in the vertical position.
Now set a square against the blade; most particularly, set it against the blade body, not the teeth. I found a nice yellow square to use in the photo which makes the operation easier to see. If the blade sits flat against the square all is well and there is no need for any adjustment. If it is tilted away from, or in towards the square, the blade must be squared up.
On most radial arm saws, this involves removing the bevel indicator plate to gain access to the adjustment bolts. After slightly loosening the bolts, tilt the motor to align the blade to the square. If you find the weight of the motor is making it difficult to control the tilting of the blade, place a block of wood under the motor body and if necessary, shim the motor (perhaps with feeler gauges) until you get the tilt adjustment just right. Once you are satisfied that the blade is square, re-tighten the adjustment bolts, re-fit the bevel indicator plate and set the bevel indicator to zero.
Setting a square against the blade
The round black disc to the right hand of the picture is the bevel indicator plate
Bevel indicator plate removed exposing the adjustment bolts.
- Check for fence-to-arm alignment.
The next step is to square the arm of the saw to the fence. This ensures that the blade will travel on a line that is square or perpendicular to the fence. Use a framing square to check the travel of the blade is 90 degrees to the fence. Note in the picture below that I have raised the framing square up on parallel bars so that the operation can be done without the blade touching the table.
Hold the short leg of the framing square firmly against the fence. Then mark a single tooth on the blade with a marker to act as a reference tooth. With the square just touching the reference tooth, carefully pull the saw head forward fully to the front of the arm, checking that the reference tooth stays just in contact with the square. A ‘third hand’ may be useful here; you can clamp the square to the fence. Clearly the blade must not be allowed to rotate during this operation. If the tooth just scrapes the square all the way, the arm is square to the fence.
If the blade veers away from, or into the square, the arm needs adjustment. The adjustment now required is done at the back of the column. Most radial arm saws have a metal bar welded to the back of the column which runs down into the split column base. Two or four adjustment nuts, usually with Allen heads will be found on the side of the column base at this point.
Squaring the blade to the fence
Here I am holding back the rubber covering
to expose the two adjustment nuts on the column.
To adjust the arm, pressure is applied against the metal bar by loosening the lock nuts and tightening the top or bottom Allen screw against the bar to nudge the arm one way or the other.
An alternative approach to this problem is to adjust the table into square with the blade by loosening the brackets under the table and tapping the table into square with a mallet. Some people find this easier. Which method you use is a matter of preference.
- Check for Heel.
Now we come to the final part of the tuning process; a part that is important but which can be confusing to newcomers to the RAS. We are happy that the table is flat and level. We are happy also, that the blade is square to the table and that the blade’s travel (the arm) is square to the fence. But this does not necessarily mean that the blade itself is square to the fence. How so? Sometimes, the yoke (and therefore, the blade) may be very slightly misaligned on the carriage. This means that as the blade travels forward along the arm it is effectively travelling on two tracks (even though the line of travel is square to the fence). The leading edge of the blade may be slightly to the left or slightly to the right of the trailing edge.
The consequence of this is that the saw-blade cuts or ploughs a wider kerf than it should and the trailing edge of the blade leaves rough and burned edges in its wake.
Heel is also a major cause of kick-back (perhaps the main cause). When ripping, Heel can push the board towards or away from the fence causing the saw to kick back and buck. This is the very phenomenon that has given rise to the RAS having a poor safety record. This is a pity. Keeping the saw properly adjusted and tuned and adhering to safe practice will prevent such problems.
A less well understood oddity of Heel, is that it can occur on the horizontal plane as well as the vertical plane. Therefore, it is necessary to check both planes. This all sounds more complicated than it is. Moreover, most owner’s manuals and books on the subject of radial arm saws only skim over this, most important of adjustments.
It will be necessary for you to ascertain where the adjustment nuts for Heel are on your particular saw. One some, they are located at the pivot point of the motor. That is, the back of the yoke; on the opposite side to the handle. In this case there are usually three bolts set out in a fanned, triangular arrangements with 120 degrees between each bolt. Here the rear motor mount can be moved in the yoke.
Vertical Heel is adjusted by loosening and re-tightening the two top bolts; horizontal Heel is adjusted by loosening and re-tightening all three bolts.
The Heel adjustment bolts that will be found on some RASs.
In this case the bolts are the black ones.
For horizontal Heel, it will be a matter of determining which direction of adjustment is required and loosening either the two top bolts slightly and tightening the bottom one by the same amount, or vice versa. Care should be taken here not to adjust the top two bolts differently from each other or the vertical adjustment may be inadvertently changed (this is why it makes sense to adjust for horizontal Heel first).
For vertical Heel, adjustment it is again, a matter of determining which direction of adjustment is required and then loosening the top bolt on one side slightly and tightening the opposite top bolt by the same amount. The bottom bolt is not involved in vertical Heel adjustment.
In other saws you may have to tackle adjustment by loosening the two bolts that set the yoke indexing (found on the underside of the yoke), to adjust for vertical Heel. Then to adjust for horizontal Heel, you have to work with the motor pivot bolt. Here, what secures the motor to the yoke is a bar that slides in the cooling fins of the motor. The bar is clamped in place by the pivot bolt. Release the bolt and twist the motor whichever way is required so that the bar slides to a slightly different position in the fins. Then re-clamp the bolt. As before, it is best to adjust for horizontal Heel first, otherwise you will have to re-visit the adjustment for vertical Heel
So, study your saw and become familiar with the particular arrangements that pertain before you attempt these adjustments.
Two ‘vertical Heel adjusting’ bolts on the underside of the yoke.
The Motor pivot bolt. Horizontal Heel is worked on from here.
Checking for Heel in your RAS.
To check for horizontal Heel (which is generally done first for reasons that will be obvious from what has gone before) make a simple jig by gluing a short dowel into a block of wood. Plug out the saw and remove the blade guard and pivot the saw so that the blade is horizontal. Lock it in this position. Place the jig with the dowel pointing upwards under one side of the blade (say, the right hand side as you face the table, as in the photo below) with the blade just touching the top of the dowel.
The jig being placed beneath the saw blade. Set it beneath the teeth.
Rotate the blade and listen for a scraping sound. Mark the tooth (or teeth) that makes the scraping sound. Now move the jig to the other side of the blade (the left hand side if you started on the right) and repeat the process. If the marked tooth makes the same sound on both sides, there is no heel on the horizontal plane and all is well.
The little jig can also be used to check for vertical Heel by clamping it to the fence and performing a similar operation to the one just described for horizontal Heel.
Checking for Heel in the vertical plane.
However, I usually use a framing square to check for vertical Heel, simply because it’s quicker. By raising the long leg of the square on a support block (see photo), the check is more accurate as a greater surface area of the blade is referenced against the square. Sighting down along the long leg of the square will immediately show up any misalignment of the blade resulting from Heel.
A view down the long leg of the square. Looking good!
De Cristoforo [R.J., The Magic of your Radial Arm Saw, ISBN 0-937558-14-1] describes a further method of checking for Heel which involves trimming the end of a piece of 2” stock in the cross-cut position and examining the resulting score marks on the end of the wood. If there are pronounced radial marks on the end of the board, the saw needs adjustment. The test should be repeated with the wood positioned on the other side of the blade. Presumably, it would take a little experience to judge the quality of the cuts in this way but it certainly seems a handy and quick way of checking for Heel. There is no need for removing the blade guard or the blade.
Unusually, De Cristoforo also recommends checking for Heel in the bevel position (i.e. with the blade tilted to 45°), presumably as a means of ascertaining horizontal Heel. As before, he suggests cutting 2” material and checking for tooth marks and making adjustments accordingly. I have not tried this method myself so cannot really comment on it further.
Kick-backs & Safety
The reputation of the RAS has suffered because of the occurrence of kick-backs. It should be noted however, that kick-backs don’t just happen; they are caused. Moreover, they are not peculiar to the RAS alone; they happen frequently on table saws as well. And of its nature, the operator is usually standing behind a table saw, right in the line of fire, if it kicks back. Maybe its serendipity, but I have had much fewer incidence of kick-back with my RAS (just one actually) than I have with my table saw over the years. It was the one kick-back event that I experienced that prompted me to look further into the causes of such events. In any case, if we eliminate the cause, then the kick-back won’t happen. For those new to wood working, a kick-back is when a piece of wood is hurled from the saw at great speed, often accompanied by a frightening bang. Certainly, when it happens, a bad kick-back is a scary experience.
Usually, the cause is stock becoming trapped or jammed between the rotating blade and something stationary such as the fence or blade-guard. It’s the proverbial story; when an irresistible force meets an immovable object….
Sometimes, stress in the wood will cause the saw kerf to close tightly around the blade. Such trapping of the blade can also cause kick-back.
Anti-kick-back pawls can help to prevent trouble and a splitter fixed to the saw can help to prevent the kerf from gripping the wood.
Stock that is kicked back can have the velocity of an arrow; this is a serious hazard. Moreover, the operator’s hand can be pulled into the blade by a kick-back if it is on the out-feed side of the blade. The best way to avoid kick-back is to prevent it happening in the first place.
We prevent and avoid kick-backs by observing a set of simple rules and by using common sense. These ‘rules’ are no-brainers really; they apply to any saw or machine, not just to the radial arm saw.
- Keep the saw in good adjustment at all times; especially ensure that there is no Heel in the blade.
- Keep the saw clean of sawdust and debris that might cause obstruction or get caught between the blade and the guard.
- Always use a blade-guard with splitter and anti-kick-back pawls.
- Keep the anti-kick-back pawls sharp so that they will dig into the wood if a kick-back occurs.
- Use a blade with a negative hook angle. Large hook angles contribute to the lifting and kick-back problem [Cliffe, R.W. Radial Arm Saw Techniques, ISBN 0-8069-6280-1].
- Keep the blade sharp.
- Control all cuts with the fence; never try to cut (cross-cut or rip) without fence support. That is, never try to cut free-hand.
- Feed stock that is being ripped straight and keep it in firm contact with the fence at all times (feather boards may help). Don’t let the stock ‘tail-wander’ in a way that would cause sideways pressure on the blade.
- Don’t cross-cut when the saw is set up for ripping (even if it’s only one little piece you have to nip off. i.e. don’t take short cuts).
- Always feed stock being ripped completely through and past the blade. Never release the stock while it is still between the blade and the fence.
- Use a push stick.
- Stand to the side of the saw when ripping; out of the line of fire of a kick-back.
- Never feed stock into the saw from the wrong direction. Stock should always be fed AGAINST the rotation of the spinning blade.
- Never reach behind the spinning blade to set up the next cut or to clear off-cuts; always kill the power and wait for the blade to stop rotating.
- When ripping make sure the overall length of the saw table (i.e. infeed + outfeed) is twice the length of the board being cut so that work is fully supported all the way. In this regard, work out your cutting list in advance and cut boards down to length as much as possible before ripping. This will keep the rips short; it is much harder to control the feed-line of a longer board.
Some other general safety rules.
- When cross-cutting, clamp the work piece down if possible (it is well worth building a dedicated clamping system for your radial arm saw. See my blog of 9.3.2016 waneyedgeworkshop.com for some ideas).
- Wear eye protection, ear protection and dust protection.
- Keep the floor swept and free from debris. Sawdust can be very slippery and you don’t want to slip and fall into the saw.
- Keep the saw table itself free from debris and tools etc.
- Never use the saw with the blade guards removed.
- Don’t overreach; keep a proper footing and balance at all times.
My clamping system in use during a cross-cut.
- Never attempt to remove small offcuts and scraps with the fingers.
- Don’t take short-cuts! Don’t take short-cuts! Don’t take short-cuts!
There is nothing new in any of this; it’s not rocket science and applies equally to all power saws. Common sense should prevail. Always think about what you are doing or about to do. Usually, the safe method also leads to the best finish and in the end, is the swiftest method. Badly thought out procedures lead to accidents and cock-ups, mistakes, frustration and wasted material.
I have developed a sliding table system for ripping that allows the stock to be clamped down during the ripping process. (See my blog entry of 9.3.2016, waneyedgeworkshop.com). I am in the process of improving this system even further and will post a blog in due course detailing these improvements. In my present system the saw is set in the out-rip position (that is, material will fed into the blade from the left hand side of the machine (viewing from the front) and of course, the blade will be rotating against the feed direction. My present system does not allow for in-ripping.
Do remember that you are responsible for your own safety at all times. The systems described here work for me, they may not work for you. Your machinery, maintenance and safety procedures will differ from mine. All tools and machines are dangerous. Always read the manufacturer’s guidelines (owner’s manual) and think carefully about what you are doing. Be safe!