i am in the middle of building a gantry type mill for machining aluminum parts, the gantry is 38" wide will two 1" a2 tool steel rods with bronze bearings have to much deflection?

If they're not fully supported, yes, they'll deflect too much.

Look at Pacific Bearing their feather shafting to get the idea,http://www.pacific-bearing.com/products/listFamilies.cfm?catID=01743E4A-C09F-1129-FCBA-8D51980DB944#
Thay also supply the teflon lined bearings.
Al.

http://www.pacific-bearing.com/products/listFamilies.cfm?catID=01743E4A-C09F-1129-FCBA-8D51980DB944#

I'm a bit confused with there "B" and "E" dimensions being different (if you click the image)

Anway, i'm also looking for steel rod. i found that precision rod (even chromed!) is usually
manufactured for hydrolic cylinders, etc. I have not requested a price yet, but i expect
they are far from cheap...
I'm looking for 1 inch (or 25/30mm) 2 length of 2.2 meter (87"). _not_ hardened, since
in need to drill and tab it to mount it on supports. I plan on drilling and taping from 2 directions (at 90 deg.), and lock-tight in M6 studs, so i can adjust in 2 directions.
I will use 4 standard bearings per mount, spaced 70deg apart.

I expect that if i just order plain steel rod, i will get something with very uneven diameter,
and the carige will just jam at some point, and be loose somewhere else.
if i understand correctly this is the same for cols and hot rolled bar.
i also found something called "cold drawn" bar.

Can anyone tell me what kind of diameter accuracy a can expect from "cold drawn" bar ?
i don't care about absolute diameter or "roundness", as long as it's the same over the
whole length.

jaap.

What I found to use is 1" pre ground a2 toolsteel round stock from the local tool & die supply shop, It comes ground to 1.013 over the whole length. and it is machinable too.
I wanted to use bronze bearings that cost 2.00 ea. or so for the linear bearings.it cost alot less.But I wander if it will work with steppers or not? they work on hydro machines that I have built before.

What I found to use is 1" pre ground a2 toolsteel round stock from the local tool & die supply shop, It comes ground to 1.013 over the whole length. and it is machinable too.
sounds good! i will try to find a local (Dutch) supplier and order it tomorrow. :-)

I wanted to use bronze bearings that cost 2.00 ea. or so for the linear bearings.it cost alot less.But I wander if it will work with steppers or not? they work on hydro machines that I have built before.
or maybe use something like oil-impregnated non-expanding platic sleves:
http://www.igus-uk.co.uk/Image7.jpg
http://www.igus.pt/xiglidurWeb/start/sub_re_drylin_d.asp?PRGR=54
http://www.igus.pt/Default.asp?LANGUAGE=E
If i remember correctly they are not that expensive, easy to replace and have much lower
friction than brass. they also make "open" ones (including mounting blocks) so you can
support the rail.
(we used them for some big stuff: http://www.marimecs.com/03c_aframe.jpg )
jaap.

..... expect that if i just order plain steel rod, i will get something with very uneven diameter,
and the carige will just jam at some point, and be loose somewhere else.
if i understand correctly this is the same for cols and hot rolled bar.
i also found something called "cold drawn" bar.

Can anyone tell me what kind of diameter accuracy a can expect from "cold drawn" bar ?
i don't care about absolute diameter or "roundness", as long as it's the same over the
whole length.

jaap.

You can get bright finish, or ground finish, shaft (C1045) which is ground (I think) to plus nothing minus 0.0005" to the nominal size on diameter and straight to a few thousandths of an inch per foot. It should be available in Europe. Cold rolled steel shaft (CRS) (C1018) is normally within less than 0.001" to the nominal size and is often straight to better than 0.01" per foot. If you have access to a lathe, dial indicator and an acetylene torch it is possible to straighten CRS to within about 0.005" per foot with a bit of practice.

You can get bright finish, or ground finish, shaft (C1045) which is ground (I think) to plus nothing minus 0.0005" to the nominal size on diameter and straight to a few thousandths of an inch per foot. It should be available in Europe. Cold rolled steel shaft (CRS) (C1018) is normally within less than 0.001" to the nominal size and is often straight to better than 0.01" per foot. If you have access to a lathe, dial indicator and an acetylene torch it is possible to straighten CRS to within about 0.005" per foot with a bit of practice.

I will use 25mm or 30mm tool steel with h9 accuracy (0.05mm), and support it at as
often as needed to adjust (and keep) it strait, so initial straitness is not a big problem.
i also received a tip from use "limbo" to use 30mm central heating tubing, which is
reasonably even diameter and very smooth, and is very easy to get. (even chromed)
jaap.