Monday, 28 August 2017

Tim's Modifications to A8 3D Printer

I have only used PLA on my 3D printer and it does what I need, so I see no reason to change.
Reading about the other types of material to use, most people say that PLA is the easiest to use.


But why modify the 3D printer?
Well, simple answer is: Getting the 1st layer correct.

The 3D Printer I bought

A very nice and cheep kit, I would recommend it to anyone.
I enjoyed assembling it and it prints very well.

So why change a good thing? If it works leave well alone.

Well, when you get the kit, it comes with a layer of masking tape on the bed ready for a print.
After a few prints this tape starts to become damaged and needs replacing.
With the right type of masking tape, the first layer of your print will usually work, the tolerance the bed has to be within, can be quite relaxed. (when I say relaxed, within 0.5mm)
The manufacturers of the kit obviously found the best masking tape for the gob, as the tape that comes on the bed works great, I only wish they had put a roll of it in the kit.
So finding the right masking tape can get expensive, as not all masking tape is the same.
After many purchases and an empty wallet, I found the Blue Homebase brand worked best for me.

Still, why change things?

The trouble I was having, with masking tape, the tack starts to fail when heated, and you need to heat the bed to stop shrinkage until the print is done, or the print will curl up at the edges.

So, I thought there must be something better than masking tape, and had a look on the web.

Yes there is.
But so expensive.

So, I thought what are they making this stuff out of, and is there something else made of the same stuff but cheaper and can be repurposed.

Yes there is.
Well something similar.

To use it we need to get the printer setup more accurate than it currently stands.
It's not a problem with the bed, that can be adjusted with the screws.
It's the X and Z supports.



These are the original 3D Printed X and Z Supports

If you examine these two part closely, like me you will probably get the impression that they are mass produced at the fastest print speed they can get away with.
As the two parts are different, you will get different amounts of shrinkage.
Not much, but enough to make a difference,
we need accuracy less than 0.2 mm. (The thickness of first layer)

Holes where the X axis linier bars go.

Take a set of Callipers and measure the distance across the two horizontal bars.
Mine are both exactly the same now, but before I did the new supports there was a 0.5mm difference.
This may not seem a lot, but you must remember the first layer is only 0.2 mm thick.

So, how did I get both side exactly the same?
I made both parts that hold the bars, exactly the same.
The differences made as separate items, then screwed together.

Although  a 3D printer can do complicated parts in one piece, I have found it is sometimes not practical to do so. Some parts are better done in pieces, this not only makes it easier to print some parts, it also enables you to change individual pieces rather than scrap the whole part.

Having things screwed together also enable you to make tiny adjustment if things don't line up correctly.

The screws I use are M3 x 10mm Pan Head Flat Tail Self Tapping Sheet Metal Screw.

The 8mm Linear Motion Ball Bearing that coms with the kit are the 45mm long ones, one on each.
I had some of the shorter ones 24mm long, so I used 4 of them, 2 on each.
My mod can use the original ones, 2 ridges will need to be removed, easy with a crafting knife.

Remove the 2 inner ridges and place the original Bering at one end

This is what mine look like, notice I have changed the position of the Jack Nut mount.




Here is a screen shot showing all the parts and the orientation to print them. You may wish to print them one item at a time. You need to make a mirror copy of the Jack Nut support.


I printed these with a top/bottom and shell thickness of 1.6mm

STL Files:



While I was dong this mod I felt it would be a good idea to make a better link for the Timing Belt.



While attaching the belt under tension, the 2 little lugs I added broke off, so you will need to remove them as well, as I have put the lugs on the (Mk2) cover.


The excess belt needs to be place in the downward direction, not upward as shown in this photo.


When you add the cover, it aligns the lower part of the belt parallel with the top part.


STL Files:





There is another modification I did to ensure that the Z axis was where it should be, was to add a spacer in the flexible joint.

If like mine, you had to fix the link at the very ends of the Stepper Motor Drive and the Jack Screw, so that the Jack Screw reached through the support at the top of the printer.

This makes the Flexible Link act like a spring.
We want the joint to flex along it's axis if needed, but we don't want it bouncing up and down.
(Well, up yes, sort of, if it hits a bit of debris, but when it comes back down, we want it to come down to the correct position, and not into your print. )

So, we need to place a spacer inside.
Something about 6mm diameter and 12mm long.
Two 6mm or 8mm ball bearings in each would be ideal.

I have drawn a sketch to show what I mean (the spacer is the blue bit).
When fastening the grub screws on the link, tighten the bottom ones first, then when you tighten the top ones, just lift the top of the link ever so slightly before  tightening the grub screws.
This will keep a little tension on the spacer inside, and ensure the Jack Screw is where we want it.


RH End Back View


RH End Front View



Motor End Front View



Motor End Back View


You will see from the front views that I have inverted the Jack Nuts and placed them at the bottom of the supports.
This means that the screws that locate the Jack screws do not take any weight, all that the locating screws do, is stop the Jack Nut from rotating.
This means they do not have to be tight, best to leave one slack and the other just needs tightening so you can move the Jack Nut side to side, but not vertically.
When these screws are set (ones that go through the brass Jack Nut), slacken the ones that hold the Jack Nut support to the Main Support on both sides. Level up both sides to the same height, then tighten them up.
You should find that the Jack Screw moves much more freely through the Jack Nut now.

For me the Jack Screws where soo free after the mod. They rattled while printing.
So, I made some anti rattle clips.

Clip to stop the annoying rattle while it's printing


STL File:


Now I can set up my 3D Printer within 0.2mm, it's time for the new bed cover.
NO MORE TAPE.
NO MORE CURLING UP AT THE EDGES.
LOVELY FLAT SMOOTH PRINTS

What is it? I hear you say.

It's simply:
 Copper Clad Glass Fibre.

Don't get SRPB, that's paper based.

The widest I could find was 200mm.
Length, I got was 300mm and I cut this down to 250mm.
The Thickness of the board I bought was the thicker stuff, 2mm thick. (The thicker the better I think)
So, I loose 10mm at the front and back, but gain 20mm on the left and 10mm on the right.

I used my plotter I made to score a 10mm grid onto the sheet. I don't think you need to do this, I just had some idea to do it at the time.


You need to take the glossy shine of the resin before using it.
I did this by rubbing it down with P120 grit wet/dry emery.
Do it wet on a nice flat surface using a block.
Do the whole surface until you see no shiny spots.

When your done and you dry it off make sure you don't touch the surface with your fingers.
The slightest bit of grease, which includes fingerprints will ruin it.
(you can see where I touched it in the photo above)
After rubbing it down and it's dry, take a small stainless steel wire brush and buff it up a little.
Do it so you don't bend the bristles on the brush but do it well. Do it like you would to buff the polish on your shoes :)
Use the brush to remove fingerprints as well.

I used double sided adhesive tape to stick it to the bed, didn't use much, just the edges and a bit in the middle. 

As mentioned before, it's a little short front and back, but overlaps the bed 20mm on the left and 10mm on the right.


Well, lets continue with the improvements.

The Timing Belt fastening under the bed could do with a better fixing.

Timing Belt Link for under the bed


With cover


Leave the Timing Belt a little long, in case you need to remove it for some reason.


In position without the cover

STL Files:



Settings

I'm only using PLA at the moment.

Bed Temperature:
I have it set at 50 deg. C in Cura. But I use the menu on the machine to pre heat to 60 deg. C. This is to aide the first layer. having the bed at 60 deg. C when while the first layer is going down gives better adhesion.
Don't go below 50 deg. C, if yo do you will find your print will pop off during the print.

Thickness:
Keep the top/bottom and shell thickness down to 1.2mm.
If you want to go thicker, yo will need to increase the bed temperature.

Be carful of high bed temperatures if you like me have stuck the plate on the bed with self adhesive tape, I plan to do some sort of mechanical fixing in the future, after all, it has a copper side things can be soldered on.




Tests


The bottom of this screw is only 12mm diameter.

The diameter of the screw at the top is 4mm and is 100mm high. wobbles slightly, but still stuck to the bed.


The screw actually works



This is just to show how flat and smooth the base of my prints are now.

After about 50 prints, the double sided tape started to fail. Rather than replace the tape, I have use for the moment, 4 small bulldog clips to hold down the PCB at the edges.
I am currently in the process of devising some thing better.
As one of the clips can't be placed at the home position and if doing a large print, one has to be carful of the clips positions.

Bought some Countersunk head screws, some springs, nylock nuts and washers.

Made some clips. (x4)

I didn't want to remove the PCB Bed in case I damaged it while doing so.
So I used my micro pedestal drill I made, to drill the holes and countersink the holes.

Using my micro drill without its base to countersink the holes.

The holes need to be drilled as close to the bed as possible. Be carful that you don't get them too close, that they interfere with the base plate.

View from underneath.
Did this at all four corners.


Before all this, my 1st mod was to make an extrusion cooler that surrounded the nozzle, as the one supplied only cooled from one side. I noticed that the plastic on the far side of the nozzle had a tendency to rise up during the print.

As I have become better at printing I am now on MK3 nozzle cooler.
I have tried to keep it as small as I can, as I like to be able to see what's going on.


Sketch I Made to make sure I got it right.


I used no support when I printed the bottom half, so I guess this print is not for the novice.
STL Files:
Top Half
Bottom Half

Take Note: This May Not be at the right height for you. It depends on what distance your nozzle is from the blower.

Oh you will need 2 screws as mentioned before to put the 2 pieces together.

The Tip of my nozzle is about 25mm from the underside of the frame.
Fitted
Oh I forgot there was an other one before this.
The screw on the top of the extruder was a little painful on the thumb and fingers.
so I made a button to go over the top of it.

The button makes it easier to press. when changing the filament.


STL File:
Extruder Button




Another mod I made was a guide for the filament, so that the stepper motor for the X axis did not have to keep pulling the filament off the reel. The extruder no longer has any force against it from the filament.


Here you can see both ends of the guide. It uses Newton's 3rd Law to transfer the force of  puling the  filament along the pipe and not interfering with the movement of the extruder.

This enables you place the reel of filament anywhere you like.


Here's a sketch to show things a little more clearly.

I have use a length of 4mm OD x 2mm ID PTFE tubing to link the 2 parts.
You will need 2 lengths (approx. 2x 70mm) of 3mm OD bright polished bar to support one of the parts at the extruder end.
Also at the extruder end you will need 3 M4 x 12mm set screws.
At the spool end I have used the self taping screws I mention above.

The reason for the bright bar at the extruder end is to allow for the filament retraction to happen quickly without any hindrance to the process.




STL Files:


When I printed these out I found that I had made the holes for the pipe a bit tight.
I had to ream them out with a 5.5mm drill bit.
The pipe can be a slack fit in the fittings.
Don't ream the hole all the way through, the pipe sits on a ledge.

Also the "Extruder End Pipe Support" should be a slack fit on the 3mm bright bar.
The 3mm bright bar should be a tight fit in the "Extruder End Mounting Bracket".

The video shows how smoothly the filament comes off the reel, and the retraction mechanism in action.





The essential Power Switch. Far better than pulling the plug in and out.
I soldered the wires to the switch and added the innards of a block connector to the housing to enable the connection of the mains lead.



STL Files:
Power Switch Housing


I also noticed movement in the bars that support the bed.
You can move these up and down slightly, which alters the gap between the bed and the head.
To over come this problem I made 4 simple springs that hold the bars in the lower position.
I made the springs out of 1.2mm dia. spring steel.

I made 2 as draw and 2 opposite hand.
1 added at each end of each bar


This is not a mod but you may find it useful.
When I am adjusting the bed level with my screwdriver.
I thought it would be useful to know by how much I have moved the bed.
So I made this little gadget that attaches to my screwdriver.

It's a Pentagon shaped ring that slides over the shaft over my screwdriver. (5 sides)
The bed is secured in place with standard M3 set screws.
The standard M3 screw has a thread pitch of 0.5mm.
Therefore if you have something that can indicate you have rotated you screwdriver 1/5th of a turn, then you know you have moved the bed 0.1mm.

Remember though: you are only moving 1 corner at a time, so you have to incorporate the principles of leverage. (moving 1 screw 0.2mm on one corner may only move the middle 0.1mm)


Extruder Cooler Mod
Sometimes I have had a little difficulty changing the filament.
Some times a bit of the previous filament gets left in the top of the feed pipe and I have had to strip down the fan to get access and remove the obstruction.

So I have come up with this little mod so that I have access all the time.

Front View


Back View
Here's a sketch to show it a little clearer

It was quite cheep to make, I only had to by 2 pieces.

First the heat transfer pipe and fins.
search eBay for:
Fujitsu Esprimo V5515 CPU Cooling Heatsink


Second was a Spacer to go between the Feeder and the Heatsink.
I shopped around for a piece of aluminium block to do the job, but the price I thought was too much.
so like always I looked for other cheaper stuff I can re-purpose.

search eBay for:
Double Extruder Nozzle Throat Pipe

I removed the tags, filed down the studs and cut off the top flange of the Heatsink, also filed 2 notches for the bolt to pass through.
I cut the Extruder Block in half.
You will also need a clamp piece about 6mm thick. (shown in sketch)
I made this from something I had laying around.
It needs to be a minimum of 6mm so that you can use the original bolts, if the clamp is thinner then you will need washers to make the right overall thickness.

I put heat transfer paste between all pieces.


STL Files:
Fan Housing
Top Bracket
Bottom Bracket

You will need longer screws than I normally use to mount the fan if you attach the guard.













I found the perfect companion for my 3D Printer at Argos.
It's the perfect size, has wheels so you can move it as and when you need it.
Argos product code: 617/2413




There are some other miner mods I have done. I will continue this soon.

Happy printing.

Tim














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