Unisaw Sliding Table Modification

Back to the Unisaw Index page

This picture shows the sliding table attachment and the rest of the tablesaw in its entirety. In addition to the sliding table attachment, there is a custom mobile base, a folding outfeed table, and a custom extension table that has a router plate in it.

Unisaw System with Sliding Table

The Problem
Over time, I have made three large cutting sleds to use on my table saw and three smaller ones. After completing a large cabinet project where I had to cut up several 4x8 sheets of " MDF plywood, I decided to search for a better way of cutting large objects on my saw. In retrospect, I view the cutting sleds as a very poor substitute for a sliding table attachment, I would have been far better off to have purchased a sliding table along with my saw.

Crosscut Sleds
A crosscut sled is an easy accessory to make and they can also be purchased in kit form from many vendors. Basically the sled is a flat carrier board with runners attached to the bottom that ride in the miter gauge slots. Usually at the front and back edges there are fences that serve to hold the carrier boards together and to create a perpendicular edge to the sawblade so you can make cuts at an accurate ninety degrees. Sometimes the sleds have stock hold-downs or adjustable fences for cuts at other than ninety degrees.

The problems with these devices are:

  1. They can be heavy, this makes them unwieldy and inconvenient to take on and off of the saw.

  2. They take up storage space when not in use.

  3. Even if the tablesaw top is waxed and the bottom of the sled has UHMW plastic tape, it is still somewhat difficult to crosscut a 24 x 96 piece of plywood due to friction and balance.

  4. When cutting large heavy pieces, the sleds are prone to tipping on the outfeed side unless special precautions are taken or an outfeed support is available.

Sliding Tables
In theory, a sliding table would allow objects to be cut much easier, better, and safer as compared to doing so with a crosscut sled. The downside of a sliding table is that they will increase the saw footprint and the guide rails can be in the way sometimes.

Modifications
The modifications I made fall into two main categories. There are those which primarily impact the crosscut fence and table, and those that affect the sliding mechanism.

The modification to the table and fence are fairly easy to do and do and make the sliding table much more useful that the OEM unit. The modifications dealing with the sliding mechanism utilize a thick steel adapter plate which would be a more difficult to fabricate part.

The primary benefits of the modifications described herein are:

  • Crosscut fence tape measure remains calibrated after removal.

  • The fence can be removed (4 sec) and replaced (12 sec) much quicker.

  • When the fence is removed, there is only one loose piece (as opposed to six).

  • The unit is easier to align.

It would be possible to perform only those modifications that did not require the adapter plate. The remaining modifications dealing with the crosscut fence and table will greatly improve the usability of the original system.

Accuracy and Performance
Aside from making the unit easier to install and align, none of the modifications described will make the sliding table attachment any more accurate that it was originally designed to be.

Improvements
After having made the latest series of modifications, there are a few aspects that could be refined further.

  • Mill a sawdust relief profile in the fence. The fence shown in the article has a piece of laminate glued to the bottom to achieve this.

  • At full extension on the infeed side there is some deflection with a very heavy load.  I've not measured the deflection but it could be reduced.

  • Add more Tee slots in the table surface, this would allow the use of other jigs or clamps

  • Add the provision for a crosscut fence system to the forward side of the sliding table. This would allow a crosscut capacity of approximately 36".

 


Sliding Table In order to solve the fence recalibration issue, it was necessary to make the pivot point of the fence stationary.  The method used to accomplish this was to use a fixed pivot arm that the fence is attached to.

The wooden pivot arm is secured to the sliding table via two Tee bolts and the plastic knobs on the top of the pivot arm.  The fence itself is attached to the pivot arm via the aluminum miter plate.  The miter plate will allow the fence to pivot through an arc of -5 through +50 (cw) degrees relative to the 90 degree home position shown here.

The fence cannot be placed in both the forward and aft positions as the OEM unit can.   With the fence in the aft position this limits the crosscut capacity to about 27 inches. If it would be more desirable to have the fence in the forward position, this mechanical concept could be flipped giving a crosscut capacity of about 36 inches.
The metal bracket in this view is the stop for the X axis pin in the pivot arm of the fence assembly.  This stop bracket constrains the fence assembly in the X axis to keep the measuring tape calibrated.

The metal plate is not a precision piece nor is its location very critical.  However, it is important that the X axis pin does not contact any component other than the Vee groove of the plate.  The fence assembly is not attached in this view.
Crosscut Fence Postion Stop
Click for more detail The fence assembly is shown detached and laying down on the fence face.  The aluminum T-slot embedded in the table surface can be seen as well as the T-bolts in the bottom of the pivot arm that slide into the T-slot when the fence assembly is attached to the table.

Click the image for a clearer view with labeled parts.
Also visible is the X axis pin in the left end of the pivot arm.  The X axis pin is a 1/4-20 bolt with the head removed. The pin will slide into a slot at the left end of the table surface and will make contact with the bracket shown above. The X axis pin and bracket limits the fence travel in one axis.  The T-bolts will constrain the fence in the Y axis somewhat but not enough to achieve a calibrated home fence position. To ensure that the fence assembly is returned to its home position, a limit plate (Y axis bracket) contacts a screw head (Y axis screw) embedded in the sliding table.

One of the best features of this fence design is that there are no precision parts in the fence calibration system. The X axis pin and the Y axis bracket and the Z surface (sliding table) combined together achieve a repeatable and accurate fence home position.
 

This is a close-up of the fence assembly near the pivot point.  The pivot bolt is a 5/16-18 bolt that is jammed from working loose from rotation by a 10-24 screw seen immediately behind it in this view.  Both the pivot bolt and the miter lever bolt have Teflon washers to reduce friction.  Because the OEM measuring tape supplied is not as readable as others.  A 1/2" straight bit in a router was used to mill the fence channels so that they would accept a 1/2" replacement tape. Although the miter plate is made of aluminum, it could have been made of 1/2" plywood.

 

Miter Detail
Flip Stop Detail  

The OEM cursor on the stop block is a fin type which will obscure half of the reading on the tape measure; a reticule type cursor allows both sides of a mark to be seen and is inherently more accurate.  A new cursor was made out of clear plastic and attached to the body of the stop block.

The OEM stop (p/n 1346805) is either too loose or too tight and will become loose over time due to the rotation of the stop.  To solve this problem a 10-32 set screw is used to jam the 1/4-20 stop pivot bolt (p/n 901-02-403-1131) to keep it from rotating once a decried level of rotational friction is set.  There are nylon washers on either side of the stop.

 

The lower guide bar is attached to the saw cabinet via two 3/8" studs that are cantilevered out from their supports by about 2 1/2 inches. In order to transfer the lower guide bar load properly to the cabinet where it belongs, two small wooden wedges are used underneath the 3/8" studs. Lower Guide Attachment
Installation Detail  

In the OEM design the top bearings control too many settings of the unit making alignment an unnecessarily complex trail and error process.   The guide bearings control slide friction, table height, and table slope.  One way to improve upon this situation is to de-couple the table Y and Z axis positions from the sliding carriage and its attached bearings.

In order to do this easily the rail and top bar are lowered by 1 " using an adapter plate.  Lowering this assembly also allows the table surface to extend over the rail (p/n 1347667) to the edge of the saw table.

The lowering plate also incorporates jack screws placed under the rail bolt stanchions that are used to very easily adjust the top bar assembly parallel to the tablesaw surface.   The adapter plate greatly simplifies the installation and alignment of the sliding table.
 

In order to keep the sliding table working smoothly, the guide bearings must be free of dust on their contacting surfaces.  Since the OEM unit did not come equipped to deal with this, dust sweepers were installed.  The sweepers are installed to the underside of the table. They are made of one inch nylon paint brushes that have a semi circular pattern cut in the bristles to conform to the top guide bar.  The handles have been cut off and they are mounted to a 1 1/2" angle bracket using a bolt in an elongated hole for adjustment. Lowering the top rail assembly makes the installation of sweepers much easier but it could be done even without using the adapter plate.  Sweepers could also be used on the lower bar but there isn't much benefit from doing so.  Visible in this view is a 1/2" thick support used to strengthen the table in the area of the T-slot.

Under Table Detail
The OEM unit is designed with a carriage stop at the beginning of its travel. The reason for locking the table in this position is to prevent the stock from being cut prematurely when loading the table with the saw on.  I preferred to lock the table even with the saw table infeed edge. A common door bolt latch is used to keep it in this position; the pin end will engage a hole drilled in the top rail.

Once the top bar assembly has been installed and made coplanar with the saw top, the lower bar is installed. With the two guide bars installed the sliding carriage (without table) is slid onto the guide bar.  The roller and bearing cams are adjusted so the carriage glides smoothly without any slop.   The bearing cams do not need to be adjusted for perfect parallelism to the saw since the table can be adjusted independently via the table attachment bolt shown.

The image below is a cross section of the sliding table along the left edge of the saw table, all the items in green are new fabrications described in the article, all others are the existing Delta components.

Assembly Diagram

Cross Section