Retrofit Of The Esta Disposable Knife System
To The Robland X31

By Paul Jordan

The Esta Dispoza-Blade™ system is designed to allow quick knife changeover with no sharpening involved - simply replace dull knives with a set of new, disposable sharp knives.

Why go with a quick-change system on the X31?

Changing and accurately adjusting the stock knives on my X31 had taken me anywhere from 60 to 90 minutes. Even with that amount of time, I usually compromised in getting the knives exactly where I wanted (within .002" to .003", which I was never able to achieve). The real problem for me was repeatability - with the stock "knife aligner" you can place the tip of the knife just about anywhere in the radius of the jig, making that setup less than repeatable. Add in the springs and you've got a repeatability nightmare. All in all I just was not happy with the stock setup.

Ordering Information and Price

I ordered the Esta knife system and received the holders, initial knives and one set of replacement knives a few days later. Total cost with tax (Esta USA and I are both in NY) came to $239.10. The three-pack of replacement blades was $32.14 of the total, which equates to $16.07 for knife changes in the future, or roughly $5.35 per new, razor sharp knife. You can order 12 packs and save even more. Hard to beat that even if you can find a reliable sharpening service.

Esta Specifications versus Robland Reality

First, the blade width of the stock Robland knife is 25mm and the Esta kit for the X31 had 18mm blade/holders. The Esta packaging is pre-printed with model #'s and which blades fit what machine, and the X31 is listed under the 18mm setup. The stock Robland springs are not tall enough to compensate for the difference between 18mm and 25mm. I called Esta and they were surprised to learn the stock blades were 25mm. Esta does offer 25mm holders, which with blades mounted come to a width of 26.5mm, which they offered to send. I had to do a little "thinking and doing" before deciding which would be best.

Ultimately I had them send the 25mm holders so that I could make a direct comparison to the 18mm holders in my possesion. With the stock springs removed, the 25mm Esta holders (26.5mm with blade) bottomed out in the knife channel at just about the right cutting height. This meant these holders would not work as all adjustability would be gone. I believe this is the reason Esta lists the 18mm setup as the one to use for the X31. However, as noted, the stock springs are not tall enough. So now two choices are evident. Acquire taller springs and stick with the stock method of knife adjustment, or replace the springs with set screws. Esta does offer a "conversion kit" to go from springs to set screws (called "Accu-Set" I believe), however they do not offer a kit for the X31 due to the small hole size for the springs. Going the set screw route would require modifications on my part.

Set Screws or Stock Robland Springs?

One of the major benefits of the Esta system is that the knife/holder is a consistent width out-of-the-box (when they get dull you switch the blades). When using the stock Robland blades, resharpening will make them smaller than 25mm, thus some type of continual adjustment (i.e., springs) is necessary. But since the Esta system is a constant width* to a fairly tight tolerance, or so Esta claims, replacing the springs with set screws would allow a one-time adjustment to the set screws, which can then be locked in place with loctite. Thus, care is taken only when the set screws are installed and not at every knife change. In theory, knives can then be simply "dropped" into place time after time, with the only (slight) variability coming from tightening the gib screws. Thus, I opted to tap the existing spring holes, remove the springs and replace them with set screws. This is where the fun began.

Modifying the X31 to Accept Set Screws

In checking the spring holes to determine the ease of tapping, two things stuck out. First, gage pins showed the holes were somewhat tapered from 0.126" down to 0.125" at the bottom. The 0.125" hole size is right between standard tap sizes. The next tap size down would require a 0.115" hole max, the next tap size up would require about a 0.135" hole. Drilling the hole open to 0.135" would have to be the first step, prior to tapping.

Secondly, and far more problematic, the spring holes are butted up against one wall of the knife cavity. This in turn meant two things - the shank of the tap (not the business end of the tap) would have to be equal to or smaller than the tap size (when typically they are larger) so that the hole could be tapped straight up and down. Also, the set screw had to be a *true* set screw - it could not have a "head" of any kind since there was no clearance.

Materials / Tools Required

  • 0.135" drill bit
  • 8-32 tap with shank turned down to the minor diameter
  • T-handle for the tap,
  • Graphite lubricant
  • 3/4" 8-32 set screws (6)


To test the reaming process, I drilled out one hole to 0.135" to see if the stock spring would "wobble" too much if I needed or wanted to go back to that setup. No problem there - a 0.010" larger hole made no difference - going back to the stock setup would always be an option. So, all six holes were reamed. Careful not to scrape the side of the cylinder head with the spinning drill!


The tap itself was a tad over 2" long, which was necessary to clear the cylinder head. With the addition of a graphite liquid to help the tapping (if you hear a squeak, your're in trouble, the tap is about to break), all six tapped fine (I did not want to snap a tap off in one of the holes as you might imagine!). All six holes were tapped in record time.

Set Screws

The next step was acquiring six 8-32 set screws. Utilizing the 18mm holders, you'll need an 8-32 set screw approximately 3/4" in length - however these are not the most common things in the world and you may have trouble finding them. The gib bar traps the Esta holder just fine, so the success of this process kind of boils down to acquiring the set screws. Now the easy parts. One of the reasons I felt this was a sound idea was that the set screws could be easily adjusted a known distance from the face of the cylinder to any accuracy desired. Since most recommendations call for the knife edge to be 1/32" to 1/16" above the cutterhead, I set each screw accordingly with the depth gage from a digital caliper, no real issues here. It took some trial and error due to the variance in the holders. You can set the screws to a general dimension, but then you have to check the knife height in the standard way (which for me is with a magnetic base dial indicator). I would say installing the set screws to a consistent height (all my blades are now within 0.002" of each other across the entire width) took approximately one hour. I found tightening the gib screws did not move the blades at all, perhaps the magnetic holders helped with that, not sure.


I decided to run tests at this point before committing to loctite (even the "break free" version). Now the fun part. I rechecked the infeed and outfeed tables for alignment and of course made sure the new knives cleared each in a dry run. I grabbed the most troublesome board from my "abandoned" pile, which was a three foot piece of Lenga. This board was notorious for displaying my shortcomings in aligning the stock knives. Ripples when face and edge jointing were much worse than any other wood, and tearout was a problem regardless of board direction.


Well, I'm not one to rave too loudly or complain too loudly, but I can't believe the difference in cuts. My stock blades were not that dull, in fact I would not have sharpened them at this point - but the Esta blades are literally razor-sharp (I have the cuts on my hands to prove it). The results were, frankly, stunning. If I were so inclined, the face jointed surface could have gone straight to finishing - no sanding required. This will quantify it somewhat - if you place a piece of glass on a smooth surface, you know how tough it is to pick up? Well, placing the face jointed side down on a flat surface came very close to that - it literally "stuck" a bit when raised. The edge joint was glass-smooth and at a perfect 90 degrees.


I would say the total installation operation took 2-3 hours. I am one happy camper at this point. Future knife changes should be a breeze, and thus I'm much more likely to tackle the chore. At a cost of $5.35 per blade, this solution is also extremely cost-effective once you hurdle the initial cost. Overall, having the information I have now, I'd do this over with no hesitation whatsoever - cost or otherwise.

* I found the Esta holders were not that consistent width-wise, IOW the holders varied up to .005" amongst themselves. Thus, per Esta recommendations, once you have the knives set you must make sure you put the same holder back in the same slot at each knife change.

Please email me with comments or questions.

Paul Jordan



© 2003 by Ellis Walentine by special arrangement with Wayne Miller of Badger Pond. All rights reserved.
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