Adding a Digital Readout to a Jointer

I have an older  6″ Bridgewood jointer upgraded with a helical cutterhead that has served me well for over 25 years. However, I’ve always found the depth adjustment gauge to be lacking – it’s a simple pointer on a scale alongside the angled infeed table ways, and isn’t particularly accurate. For many things, like surfacing rough stock, this isn’t much of an issue. But there are a few operations, like trimming the sides of fretboards to get them to precisely fit on necks, that require very light cuts, and I’ve wanted a way to reliably set the depth of cut to, say, .010″. I’ve used trial and error to do this in the past, but that’s not particularly efficient, and after putting a digital readout thickness gauge on my planer I really wished I had the same on the jointer. Unfortunately, unlike for the planer, there don’t seem to be any gauges made specifically for this application.

However, there are general-purpose digital readouts (DROs) that can be attached to pretty much any machine, and I decided to try to adapt one to give readings for my jointer. I chose a 6″ DRO that I found on Amazon that had a remote display:

Digital Readout Linear 0-150mm/0-6inch Accurate Digital LCD Digital Readout Lathe Linear Scale for Milling Machines

The attached photos show the gauge attached to the jointer, an older Bridgewood model fitted with a helical cutterhead. The steps I used to fit it follow.

  1. Determine where the end brackets need to be so the guide bar is parallel to the infeed table ways, and drill and tap 8-32 holes in the jointer base for the mounting screws.
  2. Attach the end brackets, and use these to determine how long the bar needs to be, and cut the bar to this length (mine came out to exactly 6″ – just luck). Since the bar is aluminum, it’s easily cut with a hacksaw and cleaned up with a file.
  3. Place the guide bar and carriage into the brackets, and measure the distance from the bottom of the carriage to the side of the infeed table to determine the carriage attachment bracket depth. This is the piece that attaches the carriage to the infeed table.
  4. Adjust the supplied carriage attachment bracket to provide the necessary depth for attachment as measured in the previous step. This may involve adding spacers, or as in my case flattening out the “z” in the bracket to reduce the depth.
  5. Remove the guide bar assembly, attach the bracket to the carriage, re-attach the guide bar to the end brackets, and determine where to drill and tap a hole for the screw to fasten the carriage bracket to the infeed table (mine landed exactly on the hole from the original arrow indicator, so just needed to be enlarged and tapped – as they say, it’s better to be lucky than to be good), and attach to the infeed table
  6. Adjust the table to give a 0 depth of cut, and use the zero-set button to calibrate the gauge

The whole process took just about an hour, and initial testing seems to indicate it’s quite accurate. A couple of caveats:

  • Put the batteries in first and see which orientation of the carriage gives positive versus negative measurements – you really want to have positive measurements increasing as you lower the infeed table, i.e., as the carriage moves to the right. For me, this meant orienting the carriage with the output wire on top.
  • The measurements given by the DRO need to be scaled by some factor to get the actual depth of cut, since the DRO measures the travel along the angled ways. You can determine this by using the existing scale along the infeed table, which will show how far the infeed table needs to be slid down to get a desired depth of cut. In my case, the factor was exactly 2, so the depth of cut is exactly half of what the DRO shows – i.e., if the DRO shows .050″, the depth of cut is .025″. I don’t know if this is the standard angle used for jointers, or specific to my machine, so you might have a different factor. (It would be great if the DRO manufacturers provided a mechanism to set a scale factor to make it ideal for applications like these.)

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