filament not feeding correctly, feeder alignment problem

Firstly, Mike may i thank you for being so helpful when my wife picked my printer up on Friday. Now to my problem, the filament isn't being fed at the correct rate into the extruder head. Now as an Engineer myself (10 years aerospace design, 3 years for a major tool manufacturer and 10 years+ for a gas turbine manufacturer) I set about trying to establish why this is and I believe I have found it to be one of two possible causes or even the first only made worst by the second.

1) The shaft that has the knurled portion that grips the filament floats around horizontally meaning the knurled section hardly makes contact with the filament at times causing loss of feed and a scrapped print. The shaft looks as if it floats about 1.5mm (1/16 if an inch for those still using imperial units). This could be fixed by adding a washer to the left hand side of the assembly between the left hand bearing and the nut holding the drive gear in place (this would also protect the side of the left bearing) to reduce the amount of overall float ( this would be like the washer between the right hand bearing and the hex head of the drive bolt). All left/right descriptors are as if one was looking at the rear of the machine.
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The first shot shows the correct position for the drive bolt and the second the wrong position. The filament, when the guide/pressure bearing is closed, is actually about 1mm to the left of the shown position so is missing the knurled portion entirely.
The drive gear that fits on the end of this shaft moves around an awful lot as well. Also as an engineer I was surprised to find the shaft could slip within its bearings as this means the bearings are either oversize or the shaft is undersized in diameter. This will lead to excess wear of the shaft or the bearing I/D.

2) The pressure bearing that holds the filament against the drive bolt is very tight and hard to turn and instead of helping the filament progress into the extruder it is in fact holding it back.

During a print, i did a test to show that the filament is not feeding:
1) I placed a small piece of masking tape on the filament and it did not move showing the filament was not feeding.
2) I put a mark on the pressure bearing O/D using a magic marker and it showed the bearing was not turning.


HELP!! Thank you.

 

In addition to the hobbed bolt, if that doesn't do the trick, you might also try something like this: http://www.thingiverse.com/thing:31274
As for filament ease of changing, there is a feeder called the EZ Struder that replaces the whole springy screws assembly. My printer should be going through US customs right now (hope springs) and these are upgrades in my future. I'm pretty sure that millimeter precision assembly will be more "ball park" than exact.

 

It's one thing to upgrade a purchase to get far better performance but to pay good money to rectify a design fault that makes the printer un-usable NO WAY! The extruder in this case DOES NOT WORK!! If you bought a car and the transmission refused to go into drive, you would feel cheated if you were told "oh you now need to upgrade this brand new car to make it work" well this is the same . The Guys at robo 3d need to retrofit their design to make it fit for purpose. As an engineer I have seen problems like this ignored time and time again and that's why american industry is in decline because of a "I don't care" attitude. I feel cheated and if i don't get satisfaction intend to return the printer by the end of the week.

 

Steve, while I understand your disappointment, it seems to come at the end of a series of similar disappointments in other products through time. Personally, I understood that I was buying a very inexpensive printer that was in its first development iteration and that, as such, it would likely need some modifications to get it to my satisfaction. Further, that very hobbed bolt setup has worked well enough for many and it is churning out some remarkable end products. If something this relatively insignificant is going to tip your scales so radically, perhaps you are right - this may not be the system for you. What I see is that the RoBo team has been watching closely and made ongoing improvements that are primarily being implemented in RoBo v.2 but a number of which have already been incorporated into v.1. Far from "not caring," these guys seem to be making a genuine effort to get the enterprise off the ground. Sorry you feel cheated instead of an active participant in the emerging dynamic of 3D printing.

 

OK here are the answers to your questions
1) nope no filament dust in the bottom of the feed mechanism
2) nope there are no bite marks on the unmelted filament blow the contact point with the hobbed bolt.
3) as can be seen from the photos there is no caked filament material in the hobbed grooves.
4) if i manually take controll of the print head and heat it to 190 then manualy push the fillament into the print head I get a nice regular string of material coming out of the print head.

when the printer is running it is possible to apply pressure to the filament and get the extruder head to work but

I have been involved in various forms of 3D printing for the past 20 years and come from a background in product development. Personally I want to see the ROBO 3D team prosper and I am willing to Help them in any way possible, including offering my after work services to help overcome the initial teathing problems that they might encounter. Since i live in the same city as ROBO3D is based i don't mind offering my machine as a field test and evalution unit if they so wish so they can test field modifications

I would like to know is it normal for the rear pressure bearing not to turn during opperation and to be so stiff that it wont turn smoothly when the mechanism is open?

I have noticed a number of upgrades that have a groove cut in that bearing to hold the filament in alignment with the hobbed portion of the bolt. This looks like a good partial solution.

Frankly i think using a bolt with a quite large shaft diameter tollerance to run within 2 high accuracy bearings to be a non optimal design . Bearings need a shaft diameter that is mached closely to the bearing I/D size. I am trying to find someone with a lathe to make a replacement shaft so that the shaft bearing diameters can be matched to the I/D of the bearings

Belive me i want to see ROBO 3D grow

Steve

 

Thanks Tesseract I know that with the help of this forum we can fix this problem and hopefully Robo 3d will see the mods being carried out by the users and incorporate them in the later machines

I found this item on ebay
http://www.ebay.com/itm/RepRap-Hobb...987?pt=LH_DefaultDomain_3&hash=item485a6857db

is this the correct item to retrofit my extruder? i know i need a M8 metric bolt and that i need it to work with 1.75 filament but do i need the 25 or 28mm version? it has a replacement grooved bearing that i hope will help make the design better

If it is not the correct one can someone post a link here to one that is the right one, also can someone tell me how to remove the 8mm nut on the end of the bolt that retains the drive gear as I am afraid I might damage the gear.

I have also found a work colleague who has offered to make me a replacement shaft to my own specs and I am in the process of drawing up a shaft to do the job based on a steel blank from sdp-si.com the only problem is finding someway to hobb the drive section of the shaft.

1D1 I am rarely disappointed in the products I buy or better have professionally been involve in their development, but I have seen cases where a good product has failed because of a lack of attention to detail, and I would hate to see this happen with Robo 3D. I worked for a time for a major consumer tool manufacturer developing and productionizing new designs and for the initial release of a new design a return rate of >5% was considered bad . Most of the designs I was involved with had a returns rate of <1%. One of our competitors had a similar product that had a returns rate of >20% and they went under because they refused to modify there design and learn from the bad design and improve on it.

 

Hello I had similar problem on RoBo 3D printer.
But I could recognized with my case has shown missing parts as below.
Please confirm your case try to confirm your head detail.
If you cannot see roller in movement parts side, please getting 22mm roller bearing and 8mm rid from RoBo3D.
I have purchased it from Amazon. 22mm diameter and 7mm wide. M8 bis rid also necessary.

 

You can see in yellow oval part.

 

yup i have the bearing in place, i am just about to try and do another test print, unfortunately i have been delayed by family issues.

 

Okay, so now we have a few more clues to the problem.

I tried doing a print of a 5 mm step calibration cube, even though it was not a total success it does show a lot of information. It would appear that at the start of a print the extruder is working, but after one or two layers the supply of filament runs out.



As can be seen from the above picture, the first couple of layers are being laid down correctly, but as the filament runs out the print fails.

Above the 2 failed prints you can see a section of filament that I pulled out of the extruder while still hot. The scalpel is pointing to the point where the filament was making contact with the drive bolt and clearly shows no evidence of teeth marks, even though the extruder head was fully tightened up. Also if you look closely you can see where the pressure bearing has left a slightly lighter mark on the other side of the filament.

I observed during these prints that the drive gear moves a lot on the drive bolt. Is this normal? Part of my engineering training was as an apprentice gear cutter/machinist. The situation with the gear being sloppy could lead to a situation of excess wear or premature failure.

Can anyone tell me the correct procedure for removing the drive gear as I wish to tighten up the knot behind the gear and also add a washer between this nut and the extruder head to stop the entire assembly moving and allowing the filament from disengaging from the hobbed portion of the bolt.

 

Well I finally broke down and got a new hobbed bolt on ebay

http://www.ebay.com/itm/181251969744

worth every penny just remember to spec the right distance to the hobbed section , i forgot but made a 12mm spacer to correct my error
Now all i need do is fix my sliding glass bed, i have tempory fix of using paper shims to tighten the clamps

thanks to Tesseract and everyone else