Introduction: 200mm to 425mm Bed Conversion for 3d Printer

Have you ever wanted to print something larger
than your current printer can do?

Here is a low cost option to increase the length (Y axis)
of your printer!

The Long Bed Conversion will convert a 200mm x 200mm print area to
a 200 x 425 (X,Y) print area.

I use my i2 printer to explain this instructable, but the concept can be
adapted for other 3d printer with similar "Y Axis".

Once the conversion is complete you can print your own 3d printer.
Long Bed Printed 3d Printer aka Big Red

The smooth rod clamps attached to the Y Axis smooth rods and
threaded rods should be a common area in most printers allowing
this instructable to be adapted for other printers.

  • This project does not increase the footprint of the i2.
    Larger operating area for the Y Axis needs to be provided.
    You do loose some Z Axis height with the double table.
    This printer like other 3d Printers work best on a solid, flat surface.

You can build this with a heated bed or unheated bed.
For heated bed information refer to Step 7 in this instructable:
Long Bed Printed 3d Printer aka Big Red

Some of the pictures are using the lower vertex frame of the i2 only for clarity
of the build. You do not have to tear your printer down to this level.


Stl Files are in Step 7

Here is a Video of the i2 in action:

Video of the i2 with Long Bed Printing another part.

Thanks for checking this out!

Step 1: ​Dissemble the Y Axis

Disconnect the power supply and USB cord.

Remove your Printing Surface

Disconnect the heated Bed if printer has one, set aside for now.

Disconnect the belt, the belt may be reused on lower table.
Your belt tensioner may be reused on upper table.

Remove mounting surface for Heat Bed / Printing Surface.

Remove the Y Axis Smooth Rods.

Step 2: Bill of Materials

Review the list of new parts and reuse what already have on your printer.

Bill of Materials:

1 - I2 3d printer

1 - 460mm x 220mm build surface (material of you choice)

2 - 460mm x 8mm Smooth Rod (Y Axis upper table)
2 - 230mm x 8mm threaded rod (narrow end of Y Axis upper table)
4 - 50mm x .70mm x 8mm bolts

8 - 8mm Linear Bearings (Lower Table)
6 - 608 Skate Bearings (4- Lower Table & 2- Y Axis belt drive)

1 - Micro Switch or adapt what you have for this area (Y Axis End Stop)
1m - of Gt2 belt 6mm wide (lower table - reuse yours if possible)
1 - Gt2 motor pulley 20 tooth (reuse yours if possible)
1.5m - Gt2 Belt 6mm wide - (good quality a cheap belt WILL cause problems)
20 - M3 x 0.50 Nuts
30 - M3 x 0.50mm x 20mm Screws
8 - M3 x 0.50mm x 25mm Screws (lower table bearings)

4 - M4 x 0.70 Nuts (build area)
4 - M4 x 0.70mm x 50mm Screws (build area)

20 - M8 x 0.70 Nuts
12 - M8 Flat Washers
5 - M8 x 1.25mm x 50mm Hex Cap Screws (Lower Table & Lower Motor Mount)

Printed Parts:
4 - Smooth Rod Clamps
1 - 3072 Printed Pulley (for Gt2 belt)
2 - Upper Motor Mount
2 - Lower Motor Mount Extensions
4 - Upper Table Smooth Rod Clamp
2 - Lower Table Bearing Holder
2 - Lower Table Bearing Holder (mirror)
1 - Micro Switch Holder
4 - Tall Smooth Rod Clamp (included for other builds)

Step 3: Assembling the Lower Table

Review the new printed parts list with the parts your printer has.
If your printer has the same parts, reuse them.

At this point you should have the printer disassembled down to the
Y Axis smooth rod clamps.

Set printer aside for now, and assemble the lower table.

Compare the lower bearing holder you have and the new one.
The new one has a bolt to ensure the clamp can hold the longer bed
in proper alignment when fully extended. Use the one best for this job.

Use the Short Bearing Holder for the Prusa Mendel i2 printer. The
Tall Bearing Holder is included to adapt this instructable to other printers.


Install the 4 Lower Bearing Mounts to the 220mm x 140mm lower table material.
(if you are using you old lower table, the size may be different)
See Picture, Flush with the wide side and 25mm from short edge.

Install Bearings check and adjust smooth rods for smooth movement.
Tighten Lower Bearing Mount screws recheck smooth rod smooth movement.
The access to these screws will be blocked when installing the next part.

Install the 4 Upper Bearing Mounts to the 220mm x 140mm lower table material.
See Picture, Flush with both edges. Note the orientation of the Upper Bearing
Mounts, and the direction of the 8mm x 40mm bolt.
(bolt installed other direction, the bolt hits smooth rod)

Install skate bearings and linear bearings.
The linear bearings will only slide in from outer edge.
Tighten all screws/bolts (do not over tighten)
Check and adjust for smooth movement of all Smooth Rods.

Set this assembly aside for now.

Step 4: 3072 Printed Pulley, Motor and Micro Switch

With the lower table assembly complete return to the i2 printer

Remove the idler bearing threaded rod.

Compare your smooth rod clamps with the new ones.
Use the stronger ones.

Remove the single bearing and Install the 3072 printed pulley on the
idler threaded rod, 2 nuts on each side of 3072 printed pulley.
Install smooth rod clamps with nuts.
and put the completed assembly back in the printer.
(NOTE: the 3072 printed pulley needs the large pulley side aligned
with motor), refer to picture.
The small pulley aligns with idler bearing closest to motor.


Remove the motor threaded rods (upper and lower).

you will be Installing:
3 skate 608 bearings
3 large washers
6 small washers
2 8mm nuts
1 Printed Motor Mount
to the upper threaded rod.

In this order:
8mm nut / Lg washer / Sm washer / bearing
/ Sm washer / Lg washer / Sm washer / bearing
/ Sm washer / Lg washer
/ printed motor mount / small washer / 8mm nut

add a smooth rod clamp and nuts on each end.
reinstall in to printer.

Install the 2 motor mount extenions to lowest
threaded rod on motor side with nut and washers
between them. (see picture)

Raise motor and align holes of the upper motor mount and the 2 lower
motor mount extenions. insert bolt through a washer, bolt and washer
between the two lower motor mount extensions
add a washer and nut to the bolt.
Locate the motor pulley of the
(motor mount and bearing assembly)
near the center of the threaded rod.

With the angle of the motor changed using 2 of the lower motor mount
extensions, the belt will travel around the threaded rod and be in
correct position to attach to upper table.

Step 5: Install Lower Table Assembly Into I2 Frame

With the Lower Table Assembly tight and all rods moving freely,
and the i2 frame changes made and updates still loose,
put the Lower Table Assembly smooth rods into the Smooth
Rod Clamps of the i2 frame.

Position the Lower Table Assembly in the middle of the i2 frame.
If you had yours offset to align with hot end, put back in old location.
Tighten the Smooth Rod Clamps checking for free movement of the
Lower Table Assembly as you tighten the Smooth Rod Clamps.

Align the Motor Mounts and Bearings so the motor pulley is aligned with
the center of the Lower Table Assembly.
Align the 3072 Printed Pulley so it is aligned with the Center of the
Lower Table and the motor pulley.
Tighten all related bolts / nuts related to this part of the build.

put the Gt2 belt around the idler bearing (farthest away from motor) and
the small Pulley of the 3072 Printed Pulley.
Holding the belt ends together, find the center of the lower table, mark the
location to drill a hole for a 3mm screw.
Drill the hole and put a 3mm x ,50 x.20 screw add a 3mm nut and tighten.
Put a loop in one end of your old Gt2 belt, zip tie the loop.
Now zip tie the Loop you just made to the
3mm screw in the center of the lower table.

Route the Gt2 belt around the idler bearing (farthest away from motor) and
the small Pulley of the 3072 Printed Pulley back to the center of the lower
table. Make and zip tie another loop in loose end of belt so the loop is about
25mm from 3mm screw.

Zip tie the new loop to the other loop in the belt.
Leave this connection loose, You want this to slip / jump teeth to prevent
damage to rest of the printer. After this Instructable is completed check
and tighten zip tie as needed for correct operation.

Add a washer and nut to the 3mm screw above the belt to keep belt in place.

Tighten all related bolts and screws to this area of build
Check for free movement of the lower table.

Step 6: Assembling the Upper Table & Make Changes to Firmware

You can reuse your belt tensioner attaching it to the
upper table material of your choice.
I used 6mm lexan

The 230mm x 8mm threaded rod can be replaced
with 4 - 50mm x .70mm x 8mm bolts

Slide the 450 x 8mm Smooth Rods Through the
linear bearings of the Lower Table Assembly.

Put the Upper Table Smooth Rod Clamps on the end of each of the
450mm x 8mm Smooth Rods.
Install the 230mm x 8mm threaded rod or 4 (8mm) bolts in the
Upper Table Clamps.

Attach your 460mm x 220mm build surface to
the Upper Smooth Rod Clamps.
The upper table needs to move freely from home position to the Max Position.
If the upper table will not go all the way to end, you may need to add a shim
between the Upper Smooth Rod Clamps and upper table.

If the skate bearing are not in contact with the upper table, you may
need to file some of the Upper Smooth Rod Clamp down.

Install your belt tensioner, add belt (refer to picture for belt path)
and tighten belt.

Add a printing surface of your choice.
Inspect / Review ALL Bolts and Screws.
Inspect / Review ALL Electrical connections be turning the power on.

Make changes to Marlin and Repetier Host (or firmware you are using)
Set the new length of print area.
Your home position may change.
If using auto level, this will need to be changed.
and other settings affected with this change.


Start with small moves of the "Y" Axis inspecting for proper operation
The lower belt should be loose enough to slip, avoiding damage to printer
Home the "Y" Axis and adjust lower table as needed for correct position
To Add a Heated Bed refer to:
Step 7: Heated Bed Information

Step 7: Homing, Timing of Tables & STL Files

To get full travel of the upper table, refer to picture for correct home position.
The belt for the lower table should be loose enough to slip/ jump teeth.

Home the Y Axis and check the Bearing Holder and the Smooth Rod Clamp.
If the gap is to large, move the lower table closer to the Smooth Rod Clamp.

If when homing, the belt jumps and there is no gap, move the Y Axis away
from home and move the lower table away from the Smooth Rod Clamp.

Home the Y Axis and recheck the gap. repeat and adjust as necessary.

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