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Rather than continue to hijack Joe's build thread I thought it best to post a separate question.
DC posted a link for a build where the guy had used an epoxy adhesive to build a steel frame rather than by welding. Having just read some of the latest posts an L shaped gantry seems to be favored by a few people & I wondered if building an L shaped gantry using aluminium box section rather than the extruded profile section would work if constructed this way.
I was wondering this myself, I think box section looks to be a better choice than extrusion because it's cheaper and you always have the option of pouring concrete in to improve stiffness at a later date.
I'm still a little cautious about using ally in place of steel though because it is inherently a less rigid material, if you need to triple the amount of material to get the same stiffness as steel, the cost/weight benefit has just disappeared.
Problem with steel though DC is that people have said it is not flat enough for rails to be mounted on so you are then looking at some way to get it flat for the rails, if you don't have access to grinding/machining equipment how do you get it flat enough without having it machined by someone else which is another expense.
self leveling epoxy. :)
Got to get this unhealthy obsession with epoxy in somewhere!
If you are using supported rails then steel is flat enough.
I was looking at using west system 209 super slow low viscoscity epoxy (much cheaper than the specialist stuff) and stumbled across this thread on cnczone:
New Machine Build 5.5' x 10' steel router - CNCzone.com-The Largest Machinist Community on the net!
Quote:
Originally Posted by D.C.
Interesting stuff that! Please don't get me started on another obsession.... the whole CNC thing is already difficult enough to handle without all other aspects of my life falling to pieces! Lol
I could probably just use 205 if I went down that road DC, it's that cold in the unit just now that the working life is extended considerably by the temperature lol. Probably already got enough resin so would just need to buy the 209. How would you intend setting it up perfectly level though? Guy doesn't go into a lot of detail about how he set things up before he poured the resin.
It doesn't have to be 'perfectly' level before you pour the resin, gravity gives you a flat surface on the top of the resin to mount rails on after the resin has set.
The cost of the resin works out as less than the cost of buying a decently accurate spirit level...
Yer, obviously wasn't thinking when I posted lol Must be an old age thing. I was thinking you could end up with a quite thick bed of resin at one end lol but it would be easy enough to get it close to level with a spirit level. Not short of spirit levels or laser levels so got that covered, got enough resin so really just need the hardener.Quote:
Originally Posted by D.C.
Is it just resin & hardener that you have read about DC or are people adding a filler powder or something else to help
People seem to be getting good results with just the manufacture recommended mix of 209. Then again it is a bit of a ghetto solution for people needing a flat edge when they don't already have one and are unwilling to spend hundreds/thousands to get a straight edge.
The only other way I know of getting a cheap flat edge is the method used for hand grinding optical flats, (people hand grinding their own telescope mirrors need tolerances that make machinists look like cowboys) the downside of that method is it means weeks and weeks of boring repetitive manual labour. By the time you factor in the cost of all different grades of grit and building a jig it would work out more expensive then letting gravity do the work.
People seem to be getting good results with just the manufacture recommended mix of 209. Then again it is a bit of a ghetto solution for people needing a flat edge when they don't already have one and are unwilling to spend hundreds/thousands to get a straight edge.
Not a case of being unwilling to spend the money required to get a level surface, I simply don't have hundreds/thousands of pounds so the options are more limited. Now I have something else to explore having read your last post DC thanks !!
Don't know why I didn't think of it myself, one of my customers has a business grinding optical lenses amongst other things, They bought some machinery from a liquidation auction a year or so ago that I think is just in storage in case their own machines have problems. But if any of them are hooked up & I ask very nicely there is a chance that they might let me use one of them, sure there must be something I could offer to do for them in return.