Preac Table Saw Sled & Cutting Scale Joints…
31st December 
no responses · Modelwork This is a follow-up to my previous article (A Sticky Subject) on creating accurate joints in scale models. I use a Preac Micro-Precision Table saw for cutting most of the materials for my modelwork. The Preac is an excellent miniature saw, but to make it easier to use for cutting joints with absolute accuracy I built a sled for the saw based on the sled design I’ve used for the same purpose on larger industrial table saws. The rendering below illustrates the design.
Sled design for Preac Micro-Precision Table Saw
The photo shows the completed sled in place on the Preac table. The base of the sled is .065″ T. aluminum, the guide is brass and the rails are .375″ sq. steel key stock, machined and lapped flat and true. You can just see the end of the brass slide in the table’s guide slot.
Sled for the Preac.
There were several critical points in the construction of the sled. First the brass guide had to be precisely machined to slide freely in the table’s guide slot without binding and with no side-to-side play. Secondly, the near rail had to be 90° to the base of the sled and 90° to the saw blade in order for the sled to make accurate 90° cuts. The top surface of the sled base is bead-blasted providing a slight tooth to the surface, helpful when holding small pieces of stock in place for cutting. The lower surface of the sled base and the guide are buffed and polished smooth to promote sliding on the Preac table. 4-40 flat-head cap screws were used throughout to assemble the sled.
To demonstrate the use of the sled, I used a couple of scraps of Pear wood. In the first photo below, the sled is being used to cross-cut a piece of stock to length. A faint line made with a marking knife can just be seen indicating the position of the desired cut. The stock is held in position with this line corresponding to the outer edge of the saw teeth. The advantage of the sled is that the stock is securely supported on both sides of the cut.
Cross-cutting stock with the sled.
It’s a simple matter to cut multiple pieces of stock to the same length by setting a stop on the sled rail. In the photo below I’m using a simple brass clamp for this purpose.
Brass clamp used as cutting length stop.
Dadoed Butt Joint
The first step in cutting a dadoed butt joint is to layout the joint. The first reference line is scribed on the stock using a square and the marking knife.
Scribing a reference line with square & marking knife.
Next, using the piece of stock to be set into the joint as a guide, a tick mark is made on the stock using the marking knife. Then placing the blade of the marking knife in the tick mark and using the square, a second line is scribed on the stock indicating the width of the stock to be removed for the joint.
- Locating second cut line.
Now it’s time to set the blade depth. For this joint the blade will be set to a depth of half the thickness of the stock. The stock is .125″ thick, so the cutting depth will be .0625.” This dimension is set on a caliper as shown in the photo below.
Caliper set to desired cut depth.
Using the caliper, this dimension is transferred to the small Starrett square, setting the blade to the same dimension as the caliper.
- Setting Starrett square to desired cutting depth.
Using the square as a guide, the blade depth is set relative to the top surface of the sled. Always make a test cut to confirm correct depth setting and adjust if necessary.
Setting blade height using precision square as a guide.
Now that the cutting depth is set and the desired cuts are marked out on the stock, it’s time to make the first cut, carefully aligning the stock so the edge of the blade lines up with the first scribed line. Be sure to line up the blade to the correct side of the line. The bulk of the blade should be in the area of stock to be removed. For removing stock for joints, I’ve changed blades in the saw, in this case to at .051″ W. slitting blade, which being thicker, provides for greater accuracy (less potential for any blade deflection) and quick removal of more material in fewer passes.
Making the first cut.
Next, make a second cut aligning the opposite edge of the blade with the second layout line. Then remove any remaining material in between the two saw cuts, leaving a clean and precise opening for your second piece of stock.
Finishing up the rebate.
Now it’s time to assemble the joint. Although this may seem like a long and tedious process to cut one joint, the cutting of the joint is a series of simple operations that take longer to illustrate and explain, than to actually cut the joint. With sufficient practice, it is possible to cut multiple joints simultaneously and very quickly.
The photo below shows the finished joint, prior to gluing.
Finished Dadoed Butt Joint.
Half-Lap Joint
In the next series of photos I illustrate the cutting of a half-lap joint. The joints are marked out using the marking knife in a similar manner to that done with the dadoed butt joint and the blade height is set in the same manner. Using the sled it’s possible to cut several pieces at once, speeding up the process and insuring greater accuracy. In order to help correctly align the ends of both pieces to be cut, I used a precision glass block as a stop, as can be seen in the photo below. Once again the outside edge of the blade was aligned with the marked line on the stock.
Setting multiple pieces of stock to cut rebates.
After the initial cut is made, the remainder of the stock is removed with subsequent passes over the blade as shown in the photo below.
Rebates cut for half-lap joint.
After cutting, the joint can be assembled as shown in the photo below. Using the sled and angle blocks, it’s possible to make precise angled cuts in stock. With the addition of temporary lifts on the sled surface to support the stock, it is possible to make compound angle cuts.
Half-lap joint prior to gluing.
As long as care is taken in the construction and use of the sled, joints will always come out true and square providing greater strength and precision in your construction.