On the Y axis gantries of my Longmill, the eccentric nuts used to tension the v-wheels are on the top of the gantries. Would it be better to have them on the bottom? It seems to me that as it stands, adjusting the eccentric nuts would put the spindle out of tram.
I don’t know about mills but all my 3D printers have eccentric nuts on the bottom. To me it actually makes no sense to have them on the top. The carriage is supported by the top wheels and the bottom wheels are only there to counteract any lifting action (well and to make sure there is no ‘nodding’). On my 3D printers, the bottom wheels are adjusted to just barely touching the rail. When you move the carriage the bottom wheels turn but if you put a little friction on the bottom wheels they will stop moving because they are touching so lightly.
Of course I have no clue how that translates to adjusting the wheels on a mill …
Edit: looked it up and wouldn’t you know it, the eccentric wheels are on the top.
[Resources/longmill/assembly/lm-x-axis-rail.md at main · Sienci-Labs/Resources · GitHub]
That teaches me to open my mouth before engaging the brain …
@ColonelClarence I have moved your question to a more appropriate category.
This question has been discussed many times on the forum. Search on eccentric nuts to see those topics.
Take this with a grain of salt because it’s stretching the limits of my memory but I seem to recall something about it being easier to access the top wheels played a part in the decision to put them on top.
I did a search on the forum but wasn’t able to find where I read that. If you read some of the results in that search you’ll find that other members have expressed the same concerns about having them on the top.
I have a LongMill Mk1 and the following is just supposition on my part. The original LongMill used a simpler frame design with a stiffener on the X axis.
The way that stiffener hangs down makes using the provided hex key impossible. I could cut it a bit to make it work though.
So maybe they were all put on the top originally to be consistent and just never changed. This is just some wild guesswork on my part but it seems reasonable to me.
For what it’s worth, I don’t see any problem with putting them on the bottom.
EDIT: I was thinking some more about this and…
Can the eccentric nuts be moved to the bottom? Are the top holes made larger than the lower to accept the eccentric nut? A quick look at a replacement Y axis gantry plate for my Mk1 and the top holes appear bigger. Looking at onshape for my mill and the lower holes have a diameter of 5.2mm while the upper ones are 7.32mm so I guess we’re kind of stuck with having them where they are.
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