How thick?

[lgalla]

I have been a member for a year or so and don't like generalized questions,but will make one myself.
To be more specific.On a seriously large machine like Jerry fly guy or Madvac,is 3/16" or1/4" or whatever thickness steel tube sufficiently strong for threading for the linear rails?Would fine threads be in order?At what point or thickness would be overkill.Sorry for being so vague.
Larry

[Geof]

Gut feeling answer...fine thread, 3/16 wall thickness, attachment bolts every 4 to 6 inches, torqued to about 60% of the recommended maximum.

Overkill??? Anything above 1/4" wall thickness. Get your stiffness by building a truss structure much like the flyguy did.

[lgalla]

Wow Geof,7minutes to reply.You must be on servos.Jerry is moving 1800lbs on steppers at decent speeds.Overkill [1/4"] is fine for me as the gantry should weigh in at 500lbs with a 7,5 horse colombo.[gut feeling answer]I like!!!Following paper calculations to the T can result in less than optimun results.Gut feelings from experience usually blow away paper.
The question aroused as I have HRW-21 and the supplied mounting bolts are t-n-weeny perhaps M-6 or so.I will bug you some more on Gut fellings later.
Thank you mucho!
Larry

[lgalla]

How square is square?
I am a woodworker but have various pieces of steel about the shop.Checking 4'X4" steel angle it is far from square,ditto for channel.I see why or the purpose of epoxy joints to resist stressing the metal.Being the surface plate guy I assumed I could use S/P technology
to my advantage.Settling on 2-2by4's for the gantry spaced for a ballscrew in the middle I thought what a good thing to use the surface plate epoxy for accuracy.
The two by fours samples are flat and square and epoxy joints are unnessary.Is this just a fluke?Or is steel tube generally flatter and square than angles or channel?I half expected the 4" dimension to at least be bowed in.Perhaps when I file the order I will receive the inaccuracies I expected.
Are A36 tubes more accurate than other shapes?Gut felling answers are welcomed.
Larry...

[Geof]

Didn't make this one in 7 minutes due to being at a wine appreciation class.

What you should due for your tube is go and see if the supplier will let you check their stock and select the best; hollow structural steel can vary a lot. I have used many feet of 2" x 2" x1/8" and sometimes a shipment will be square to within better than .01" other times as bad as 1/16". We cut the tube into 2" lengths to make little bevel gear boxes so square is important which is why we measure it.

[lgalla]

Like going to Home Depot and selecting the best 2X4's?I am sure the steel guys would laugh if I requested to sort out 20' 200lbs 2X4's.Hopefully I will get good "run of the mill"tubes and not require many epoxy joints.
I am amazed that members are hand drilling and tapping rail mounts with success.THK says the LM guides can absorb some miss alignment.How much I don't know,But perhaps this is why members are having good results by hand.I would assume if your machine is extremely rigid this requires extremely accurate drilling and tapping as the frame will not "give".
I have seen lots of alignment schemes with clamps and tools for rail trueness.If the mounting surface is milled or leveled with epoxy half the alignment problem is solved?True?If so a scribed centre line should be all that is needed to get a true master rail.
Larry

[brunog]

Originally Posted by lgalla I have been a member for a year or so and don't like generalized questions,but will make one myself. To be more specific.On a seriously large machine like Jerry fly guy or Madvac,is 3/16" or1/4" or whatever thickness steel tube sufficiently strong for threading for the linear rails?Would fine threads be in order?At what point or thickness would be overkill.Sorry for being so vague. Larry

Larry,
Ideally the thickness of the piece to tap into should be equal to the bolt nominal size i.e 1/4 thick for 1/4-20 bolts etc... Worse case scenario is that you need to place Nutsert type inserts or self clinching nuts depending on how the drilled hole can be accessed.


Best regards

Bruno

[mxtras]

Check this site out:

http://www.futek.com/boltcalc.aspx

It has saved me countless hours of calculations over the last few years.

Scott

[Glacern]

Tubing thickness is important, but not so much for strength in this case. Smaller linear rails typically have ~60mm bolt spacing for rigidity rather than raw strength. Can't go wrong with thicker materials though. I'd go as thick as possible just for stability.

As for squareness, don't expect it to be square at all. Not quite as bad as aluminum extrusion, but not great either. Certainly not as bad as channel or angle. That stuff is garbage for anything non-structural.

Bolting/welding on an extra piece of flat bar to a tube (and either shimming or machining it flat) is a must if high accuracy and low friction is what you desire.

[lgalla]

Thanks guys for all the help.These are questions to help fine tune a design for a 5X10 router.I have spent the last 8 months on the epoxy granite thread,Ignoring what I want to achieve.Unfortunately all the Zone threads and posts I saved over the year were lost.I would like to build with no welding,using epoxy joints and E/G where useful.
An absolute must is another axis or Y carriage for a drill.A CNC router without a drill is useless to me.Upon drafting a design,[no CAD skills]It appears the gantry would have to be 8'long to cut or drill a 5'sheet.Any cool ideas for a drill?Adding 3' to the gantry ups the cost considering the price of linear rails and ballscrew.If their is noway around it,so be it I will build an 8'gantry.
Thanks again
Larry

[brunog]

Larry,
Why add a drill, you could drill and cut with the router and a router bit that is the the size of the smallest diameter hole you need to make.

Me confused!!

Best regards

Bruno

[lgalla]

Bruno, Confucius say"Baseball is wrong - man with four balls cannot walk"
Bruno,I am not CNC'd and have 2large Makita routers,2 monster porter cables and 2 makita trimmers.The idea is I don't like to change bits.One router cuts circles,one trims,one cuts from templates,one trims arborite etc.The bit or the smallist drill hole is 5/16 which in 18mm birch would probably result in 200ipm or less.Tool change is necessary at ten grand or at least a spindle and drill.My workers can blow away a CNC at 200ipm with a table saw and pin router.As a hobby router any ipm is sufficent as its cool or fun.A hundred grand router is so fast you have a guy just watching it to unload parts when finished.Hopefuly a hundred grand router can be self made for 20grand.
gotta get back to the Bradors.
Merci Bruno
Larry