Preac Table Saw Restoration

[Ray Dunakin]

That saw looks really handy! If I ever get my garage cleaned out enough to make room for it, I might get one.

[Lawton Maner]

Ray:

     You might look into the Barnes Modeler's Saw.  My wife gave me one a decade ago and the stock of all 3 of the major suppliers of basswood in the US and Canada dropped 25% overnight.  With the optional micrometer to set the rip fence it can cut O scale 1 x 2 stock.  For dressed lumber that is 0.015" x 0.030" and do it repeatedly.  I have also cut balsawood thin enough to read through.  Most of the time I use a 24 tooth carbide tipped blade, when I need to cut really smooth pieces, I switch to a metal working slitting blade.

    The only problem is that the blade doesn't tilt.  The body is totally enclosed and comes with an attachment point for a vacuum.  It also has a crank to raise and lower the blade.  Over the years as a result of feedback from his customers, Barnes has added accessories to the saw to make it do more tricks.

     Normal denials of connection entered here.

[WP Rayner]

I mentioned a few posts ago that I had added a simple blade height adjuster to the Preac. Pictures below show it. It's simply a length of 10-32 threaded rod that passes through a threaded hole in the blade support arm between the pivot mount and the blade arbor bearing housing. I added a brass knob, salvaged from something years ago. The opposite end of the threaded rod bears against the underside of the table. Adjustment is simply a matter of turning the knob to lower the blade before locking it in place on the pivot. In the first photo saw is standing on its end to get a better view of the mechanism, second photo, saw is in its normal operating position.

[WP Rayner]

This is how I make angular cuts on the Preac, other than 90 degrees. The Preac came with a simple crosscut fitting (first photo) which slides in the channel machined into the top of the table. The angle is set by loosening the cap screw, setting your angle then tightening the cap screw to lock it in place. While this works, it's difficult to set angles precisely. You can use a small precision square, such as those made by Starrett to set 90 or 45 degree angles. Anything else is trickier unless you have a protractor head for a precision combination square, again such as the one made by Starrett. To solve this issue, I use precision angle blocks in combination with the sled to make precise angular cuts. Precision angle blocks usually come in sets. The set I have has 12 blocks in the following degree increments: 1/4, 1/2, 1, 2, 3, 4, 5, 10, 15, 20, 25, and 30. Given the combination of blocks it's possible to create almost any angle. I purchased it many years ago from MSC Industrial Supply https://www.mscdirect.com/browse/Measuring-Inspecting/Calibration-Layout-Machine-Setup-Tools/Layout-Setup-Tools/Angle-Blocks-Sets?navid=12107957.

The second photo shows the basic setup I use, in this case making a hexagonal frame. The selected angle block is set on the sled, tight up against the rail of the sled (which importantly is exactly 90 degrees to the saw blade.). I hold the block in place with a short piece of double-sided tape. Note that the end of the block does not extend into the path of the blade. I cut the stock pieces a little longer than desired and then cut one end of each piece at the desired angle while leaving the pieces a little longer than the desired finished dimension. It's helpful to use a scrap piece of wood between your stock and the angle block so that the saw does not rip out the point of the cut on its way through. This scrap piece must have smooth parallel surfaces though, otherwise your cutting angle will be incorrect. Once all pieces have had one end cut, I then set the desired final length of the cut by adding a stop to the angle block, in this case the 1/4 degree angle block held in place with another piece of double-sided tape. Then it was a simple matter to cut the the pieces to their final length by placing each against the piece of scrap stock and up against the stop.

The third photo shows all six pieces held crudely in place with little pieces of scotch tape on the underside (not an accepted assembly method   ). When properly assembled, all pieces meet precisely without any gaps between the ends. Next exercise is to recreate the hexagon with proper joinery so it can be glued up.

[WP Rayner]

Opted to make a pentagon frame with half-lap joints connecting all five pieces. I cut the needed pieces from some scrap stock, plus a couple of extras in the event of messing up one of the cuts (always recommended). I used a 15 degree angle block to make all the cuts, again using the 1/4 degree angle block as a stop block for cutting the pieces to their final length. Both blocks were held to the sled with small pieces of double-stick tape. To cut the half-lap joints, I used a short piece of the frame stock set against the stop block to set the width of the half-lap joint, as shown in the first photo, again using a piece of scrap stock (green piece) between the 15 degree angle block and the frame piece being cut to prevent the outside point being ripped out. After adjusting the blade height to .045", half the thickness of the stock, I cut all the half-lap joints. Second photo shows the pentagon frame fully assembled and glued up. Using the half-lap joints creates not only a geometrically accurate pentagon but an assembly that is quite strong for its size. The purpose of all this was not specifically to make a pentagon, but to show that using a precision saw such as the Preac and proper set-up tools, it is possible to adapt traditional real-world woodworking and construction techniques to model work, ensuring accurate and strong construction.

[Lawton Maner]

Paul:
     Can I use a model railroad power supply to provide the electricity?
     
     Can I use an iron container as long as the piece to be cleaned isn't touching the container?

     I have a couple of older table saw blades which have become rusty and want to clean them up.

     All help is appreciated.

     WLM3

[WP Rayner]

Paul:
     Can I use a model railroad power supply to provide the electricity?
     
     Can I use an iron container as long as the piece to be cleaned isn't touching the container?

     I have a couple of older table saw blades which have become rusty and want to clean them up.

     All help is appreciated.

     WLM3

Yes you should be able to Lawton. The power needs to come from a low voltage DC power supply, anything less than 24 volts, so an MR power supply should work, certainly worth trying. And yes you can use an iron container as your sacrificial anode. Anything steel or iron will work, i.e. short length of scrap rebar, however the process will be quicker if your anode surrounds the item you are trying to clean of rust. The anode will be partially eaten away in the process, so use something you don't mind eating up. Graphite rods or plates can also be used, though likely harder to find. Remember that everything has to fit within a larger plastic or non-conductive container. And yes, you can't allow the saw blades to touch the sacrificial anode, very important.

[Lawton Maner]

Since I have a couple of rusty table saw blades to clean, placing them flat and insulated from the container would work on one side at a time. 

[Bernd]

Hi Paul,

I've read through this thread and am interested in how the saw blade height adjustment works. I would appreciate it if you could post a picture of the underside of the saw showing the mechanism. I'm thinking of building a saw this coming winter and need to know how the blade height adjustment works.

Bernd

[WP Rayner]

Hi Paul,

I've read through this thread and am interested in how the saw blade height adjustment works. I would appreciate it if you could post a picture of the underside of the saw showing the mechanism. I'm thinking of building a saw this coming winter and need to know how the blade height adjustment works.

Bernd

Bernd:

Here's a shot of the underside of the table. The height-adjuster screw passes through the pivoting plate that holds the saw blade armature. The end of the screw bears against the underside of the saw table. It can't raise the blade but can lower it to the desired height. I had thought of machining a small fixture that would capture the end of the screw on the underside of the table, keeping it in place while allowing it to turn, which would then enable the screw to raise and lower the blade. However, it didn't really seem necessary as I always set up the saw with the blade at maximum height then adjust it down to the desired depth using a depth micrometer referencing off the table top. Once set, the blade is then locked in place by tightening two allen-head cap screws at the ends of the pivot spindle. Hope this is of some help...

[Bernd]

Thank you very much Paul. It answers my question of what the whole spindle works looks like.

It looks like it would be easy to build now that I see how the saw spindle pivots.

Bernd