This guide shows how to use the Prusa Leveling Guide plugin in OctoPrint to check and tune the bed level on the Original Prusa MK3.5 / MK3.5S.

The method is especially useful if you use a Nylock Mod or Silicone Mod. These mods replace or modify the original fixed bed mounting points, allowing the heatbed to be adjusted more precisely. The goal is to reduce height differences across the print surface and get a more even first layer.

Without a visual guide, tuning these mods can be slow and annoying. You usually have to read mesh bed leveling values manually, interpret them, make small mechanical adjustments and repeat the process several times.

With the Prusa Leveling Guide plugin, the measured mesh is displayed directly in OctoPrint. This makes it much easier to see which areas of the bed are too high or too low and which adjustment points need correction.

This guide is based on a modified / PR build of the plugin, because the regular plugin version did not originally support the MK3.5 / MK3.5S Buddy firmware output properly.

Note: This guide uses the Prusa Leveling Guide plugin in OctoPrint. If you prefer the manual method without the plugin, you can still use my previous manual MBL guide for the Prusa MK3.5 / MK3.5S:

Why use a Nylock Mod or Silicone Mod?

The stock bed mounting system is usually good enough for normal printing, but it does not allow precise manual adjustment of every bed point. If the heatbed is slightly uneven or tilted, the printer compensates with mesh bed leveling.

That works, but it is still better to start with a mechanically flatter bed. A flatter bed means:

• more consistent first layers
• less Z compensation during printing
• better large-area prints
• fewer problems with corners being too high or too low
• easier troubleshooting when first layer issues appear

The Nylock Mod and Silicone Mod both add mechanical adjustability to the bed. The idea is the same: adjust the height of the individual bed mounting points until the measured mesh is as flat as reasonably possible.

Nylock Mod vs Silicone Mod

Both mods have the same basic goal: making the heatbed adjustable.

The Nylock Mod usually uses nylock nuts and nylon spacers under the bed. By turning the screws, you can move individual mounting points up or down very precisely.

The Silicone Mod uses silicone tube spacers instead of fixed spacers. The silicone can compress slightly, which also allows the bed height at each mounting point to be adjusted.

In practice, both methods can work well. The important part is not the mod itself, but measuring, adjusting and repeating the process until the bed is reasonably flat.

My personal recommendation: Nylock Mod

Personally, I recommend the Nylock Mod.

I have been using it for years without problems. If installed correctly, it is precise, stable and reliable.

The important part is to tighten the nylock nuts correctly: tight enough so they cannot loosen by themselves, but not so tight that the bed is no longer adjustable. The bed must still be adjustable in small, controlled steps.

That is why nylon spacers are important in this setup. They are placed at the nylock nut side and help keep the nylock nuts properly positioned while still allowing fine adjustment.

The Silicone Mod is easier and can also work well, but for my own printers I prefer the Nylock Mod because it feels more precise and mechanically stable.

Why use the Prusa Leveling Guide Plugin?

Manually reading and interpreting mesh bed leveling values is possible, but it is slow and easy to misread.

The plugin makes the process much easier because it:

• reads the MBL data from the printer
• shows the result visually
• helps identify high and low areas
• makes repeated adjustment cycles faster
• is easier to use than manually copying values from the terminal

For tuning a Nylock or Silicone Mod, this is exactly what you need: measure, adjust, measure again.

Requirements

For this guide you need:

• Original Prusa MK3.5 or MK3.5S
• OctoPrint installed and working
• USB connection between OctoPrint and the printer
• The correct printer settings in OctoPrint
• Modded Prusa Leveling Guide plugin for OctoPrint
• Nylock Mod or Silicone Mod installed
• Basic understanding of mechanical bed adjustment
• Clean steel sheet
• Normal printing temperatures for measuring

This guide assumes that your Nylock Mod or Silicone Mod is already installed. It does not explain the full mechanical installation of these mods.

Installing the modded Prusa Leveling Guide Plugin

For convenience, I provide the modified plugin ZIP file used in this guide. You can install it directly through the OctoPrint Plugin Manager.

DOWNLOAD: Octoprint – Prusa Leveling Guide for MK3.5 / MK3.5s

Installation:

1. Open OctoPrint.
2. Go to Settings → Plugin Manager.
3. Click “Get More”.
4. Scroll down and upload the plugin ZIP file.
5. Install the plugin.
6. Restart OctoPrint.
7. Reconnect to the printer.

Set up the Prusa Leveling Guide Plugin

First, we need to configure the plugin correctly in the OctoPrint settings.

Prepare the printer

Before measuring the bed, make sure the printer is in a realistic printing condition.

Recommended preparation:

1. Clean the nozzle.
2. Clean the steel sheet.
3. Install the steel sheet you normally use.
4. Heat the bed to your normal printing temperature.
5. Heat the nozzle to a normal first layer temperature.
6. Make sure there is no filament blob on the nozzle.
7. Let the printer sit at temperature for a few minutes.

Run the First Mesh Measurement

Open the Prusa Leveling Guide plugin in OctoPrint and start the mesh bed leveling measurement.

The printer will probe the bed and the plugin will display the measured mesh visually. This gives you a much clearer overview than reading raw values from the terminal.

I always set the display to degrees. That’s the easiest setting for me to adjust.

Do not focus only on one single number. Look at the overall shape of the bed. A slightly tilted bed is usually easy to correct. A twisted or uneven bed may need several small adjustment cycles.

Important: Do not try to force a perfect 0.000 mm result. That is not realistic and not necessary. The goal is a reasonably flat bed and a consistent first layer. For my own setup, I usually aim for approximately 0.035 mm or better.

Adjusting the Bed Points

After the first measurement, adjust the bed mechanically depending on your mod.

For the Nylock Mod, adjust the screws / nylock nuts carefully in small steps.

For the Silicone Mod, adjust the screws so the silicone spacers compress more or less at the required points.

Make only small adjustments. A small turn can already make a visible difference in the next mesh measurement.

Adjust one point at a time if possible. If you change too many points at once, it becomes harder to understand which adjustment improved or worsened the result.

Repeat the Measurement

After each adjustment, run the measurement again in the Prusa Leveling Guide plugin.

The workflow is simple:

1. Measure the bed.
2. Check the visual result.
3. Adjust the required points.
4. Measure again.
5. Repeat until the result is good enough.

Do not overdo it. Once the mesh looks reasonably flat and your first layer is consistent, stop adjusting.

Final First Layer Test

After the bed looks good in the plugin, print a first layer test. It is optional, but recommended.

Check the corners, center and edges of the bed. The lines should be consistent and stick well without being too squished or too loose.

If the first layer looks good, the adjustment is finished.