Backward stabilization of a Z-axis (with image)

[Johannsen]

Hi,

I'm trying to build a Z-Axis for mounting a camera to it. Overall weight would be around 20-30kg that's needed to be lifted.
Now I'm struggling at a certain point of decision. I have 2 HGR20 steel linear rails with a length of 1200mm. Those I want to attached with M5 screews to a 12mm aluminum 5083 plate. Each 60mm the rail is attached with a screw. On the back of that plate I considered two pieces for stabilization which I would mount with M4x20 countersunk head screws every 60mm or 120mm. I have now two options:
1) placing the stabilization right behind the rail
2) or on the edge of the plate.

my thoughts:
2) is easier to aligne
1) maybe more robust? but it may make the plate/underground more uneaven and so the linear rail?

What would you suggest me? I'm having hard times to decide what's best?
Thanks a lot, Max J

[ Specified attachment is not available ]

[Overspeed]

Hello

First : how do you proceed to make you U beam that an extruded profile ? or a welded parts in 3 pieces ? you can get a far better stiffness by using a rectangle extruded parts

this type of profile '' rectangle with radius '' exist in 6062 T6 or at least 6000 serie heat treated with is far more stronger than the soft 5083 including for drill an tap

https://www.aluminumextrusion-profiles.com/china-powder_painted_rectangular_aluminum_extrusions_for_furniture-1200441.html

Regarding the load depend where are the rest / support contact and how many you have

Regarding your rails , you need to bed them with epoxy putty as ''devcon putty''  to compensate your rail defect IF you screw hard steel rail on aluminium surface you will generate strain

You shall also use thread insert as helicoil OR drill through and use small aluminium ( as 2017 or 2014 alloy ) bloc drilled and tapped to handle the clamping force

Regards
OS

[Johannsen]

Hello,
thanks for your reply! No it's not extruded, I have ordered some fine-milled flat aluminium plates and my idea was to mount the support pieces with M4 screws every 60mm or 120mm

[Overspeed]

Hello

You will get nothing as stiffness and on flat raw extruded long parts they will never match perfectly , extruded hollow beam are available at low cost as that a common supply for industry .

Other problem 5083 have a low tensile level so helicoil are mandatory to do not pull off the threads under strain as your camera is in the 25 kg so not a DSLR weight

A solution if you want to use flat in 5083 you can perhaps use fiberglass / carbon composite inside your U beam



Regards
OS

[Johannsen]

Hello,
ok, yes the thing with helicoil is noted. As I already have those material I would like to give it a try. My milling machine is built by a mechanical engineering prof and he basically used the same material. Although the z-axis is only half the size but on the other hand needs to be withold much more force when milling.  The z-axis of the milling machine is just a 25mm thick 5083 plate
The  fiberglass / carbon composite is a good idea if it's still not stiff enough for the purpose 

[Overspeed]

Hello

when you will proceed of the assembly you can use Loctite 648 as glue between your parts , that make extremely tough assembly and that will compensate surface defects

Another possible improvement as you have your raw material is to use square 2017 or 2024 in the inside corner and screw in this square parts you will increase the stiffness a bit and be allowd to screw in strong alloy

Regards

OS

[Johannsen]

Hello
ok thanks for the tip. It's a pity I didn't order harder material. Thought that 5083 would do it as my milling machine is made out of it too..next time.

What would you say where to place the supports? Directly on the backside of the rails or on the edge of the base plate? (if there is any difference)

[Overspeed]

Hello

The material specification is a primary factor I agree than even plywood can work .

But from my personal background before to spend hours in machining I try to optimized the design and the material if the cost increase is negligible .

U beam is sensible to flexure and more to torsion effect IF your beam is nor strongly linked / fixed to a stiff support / bench as the question is :

Does your beam is just use a free beam just standing on a table / rest or strongly maintain / linked to the table by bolts and nuts as in this case the stiffness is the stiffness of the beam + table

Regards
OS

[Johannsen]

Hello,
yes your right with hours vs. money..
It will be fixed in an 3060 item profile frame.

[Doctorandus_P]

It seems grossly overdimensioned for an (even 25kg) camera. How much strength and stiffness do you need?

I also don't like working with aluminimum too much. I don't even know how to spell that name.
A relatively cheap and still strong and stiff construction is to first make a box out of plywood or MDF, and then glue a piece of angle steel (for example 30x30x3mm) on the corners. The wood is mostly to keep the steel beams apart, and 3mm thick steel is just enough to tap M5 holes in for the rails.

[Overspeed]

Hello

As your frame with be fit on a 30x60 extruded rail , your total stiffness will far higher that the drawing you have displayed in the first post

For Plywood the problem is the surface compression and dont forget than a wood is not another , some plywood fully injected of resin as the plywood use for concrete mold ( black plywood ) are acceptable for a lot of DIY project .

Remember that some WWII airplane was made partially in plywood as the Horten 229 and the DH 98 Mosquito was built in wood

Regards
OS