Gallery, Projects and General > The Design Shop
Portable milling/grinding machine for machine way reconditioning
PekkaNF:
Pete....Looking for a hobby, not profession.....Hmm. if i retire on country and fill one barn with old slow oversize tools.....
Hanermo. Thank you for your pointers. I'm working on same size of envelope.
Luckily I have one real designer to help me with forces, deflections and such, because even I have a cursory knowledge on these things I'm too thick to be able to calculate them correctly. He can not only calculate, but he has these on his head and I make question like. I want to make a hydraulic broach of 4 tons of maximum force and I need a beam of 70 mm wide, 20 mm bolts on both ends - 250 mm apart and hydraulic cylinder rod of 25 mm must go trough it. How much I need thickness for it. he calculated/questimated few key figures and came out result that was very close to calculated one and exactly the prefered dimension I went to buy on junk yard. I could not solve those on few minutes no matter what I had at my hand!
Nevertheless, there is always some surprices.
Pekka
PekkaNF:
I think I will lash up something Hanermo said, I'm going to try it first on scrap or something whole less critical to try it out and measure what sort of stuff it will be capable of doing.
I did measure a little of floor quality MDF and bit over 22 mm thick is not even near rigid enough to mount anything. But I can saw few strips and when deep beam is mainly on compression it looks rather doable, based on hasty measurements and numbers I am finding on MDF mechanical properties. My concern is now on how stable it will be....mainly on moisture. Looks like there are some P-grades and some are more resistant on moisture than others.
I basically could buy some, make small body that will fit on surface plate and easily check if it stays straight any time.
Pekka
Pekka
PK:
Re reading, I realise I may not have conveyed the correct message in my previous post.
When I sugguested Hiwin linear bearings, it wasn't to construct a grinding jig. I was thinking about attacking the ways with an angle grinder, slapping a couple of cups of metal filled epoxy on them and bedding the linear bearings in as replacements for the dovetails...
You gotta think big, that's the key...
:-)
PekkaNF:
Hi PK, you are right on thinking "big". That would do, specially if I could glue the whole thing upside down over a very big surface plate.
My reluctance stems due to fact that I work for a comppany that uses linear rails and bearings all the time to build machines and there is a learnig curve. Anyway, if you build something like 9-20 m long and 6-12 metres wide machine that has multiple ways every and each direction. On welded and machined frame. I know that the frame is not straight, but linear machine ways are machined pretty straight before installing the linear ways there. Because the rails are not straight either and no long linear ways is made out of one continous piece, but segments, there is a methology.
Unfortunately we have no more manufacturing on our location, therefore there are no extra pieces floating around.
On short distace linear way is pretty straight, but usually a large r, that they are easy to fit on stiff straight surface. Nothing magic there everything usefull is on linear bearing assembly and mounting instructions.
It is really not that big problem if they can be mounted on relatively flat structure, if gringing flat ways on same axis...who cares about 0,1 mm arc on sideways on 1,5 m distance - when it is on same plane than flat ways. Dovetail problem could be reduced to same problem when the dovetail flat is jigged ont same plane with ways.
Only problem here is that I don't have 1,2 - 1,5 m long linear ways at my disposal. Could buy them, but it would make pretty expensive rig for a one off. And I have no plans for a CNC hobby now.
I have a plan of buying some metres of key stock, that has been rolled into standard spesification and glue it on a frame. Have to device a method, I don't have a big eneough flat plane to rig it straight on one go, I have to think somehing.
I know the spesification, it's not great, but least is not bigger tha on bad grinding spindle. Have to keep eye on big picture here, no point of chasing the last 0,01 mm/m if something else produces bigger error. Local 0,01 mm I can scrape, but 1m long and 50 mm wide area of 0,5 mm are I can't.
Pekka
PekkaNF:
Bit testing shows, that key stock over really deep section of the MDF might just do.
Has anybody done anything small succesfully out of epoxy concrete (granite/mineral)?
Found some links and lot of enthusiam, but very little end results and practically no long term follow up. This might be canditate for it :lol:
Something like this, but whole lot crappier for "cross slide":
If I understand correctly, it's about aluminium density, compression strength is enough, tensile strength sucks and absorbs vibration about 3 times better than cast iron. Values to very good hobby grade mix.
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392008000400003
"According to Ashby & Jones13, granite has a density of 2.6 Mg/m3, a Young Modulus of 60 to 80 GPa, a tensile strength of 23 MPa and a compressive strength of 65 to 150 MPa."
Aluminum alloy (7075-T6) density of 2.7 Mg/m3, a Young Modulus of 70 GPa, a tensile strength of 510–540 MPa.
Pekka
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