Idler Rails and Assemblies

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ray_parkhurst
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Idler Rails and Assemblies

Post by ray_parkhurst »

I picked up a nice group of HiWin and Nippon Bearing (NB) idler rails, and can make them available to forum folks interested in stabilizing their systems. These can help to stabilize most any type of linear actuator, such as THK/Misumi/HiWin, or WeMacro/StackShot/MJKZZ, and can also be used with manual rails. I've shown several examples of such assemblies on these forums. Search for "idler rail" to see some examples.

The ones I just purchased are 215mm long, and I can supply either a single or dual carriage with them. They are "7" series, so the carriages are very small, only 7mm high. This enables them to be used in many ways that larger types may not support.

Usually a single idler is used to stabilize the system against movement in the "pitch" and "yaw" directions, but a second rail can be added to further stabilize against "roll". Thus a stable, moving "platform" can be built if needed or desired.

I can sell these for $12 each with one carriage, or $17 each for two carriages.

I'm also contemplating building subsystems that would include a THK rail with one or two idlers. PM me if you are interested in such a subsystem, or if you would like something custom developed for you.

Edited to add: I have also picked up a group of 155mm idler rails, also from HiWin with a couple from NB. The shorter length is useful for shorter THK rails and shorter bases and plates as shown in the drawings I created below.
Last edited by ray_parkhurst on Tue Nov 16, 2021 6:11 pm, edited 1 time in total.

ray_parkhurst
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Re: Idler Rails and Assemblies

Post by ray_parkhurst »

I sketched a few designs with KR20 actuator rails plus MGN7 idler rails. I think that attaching the actuator directly to a 40-series 8020 extrusion (with a 1/4" spacer) seems a good choice, rather than my previous method of attaching to an Arca plate. I don't see the need for movement of the entire system along the extrusion, as long as there is sufficient movement available from the rail plus clamps on the upper Arca plate.

The options are:
18" or 24" Extrusion (to accommodate different length KR20 actuators and MGN7 idlers)
150mm or 200mm KR20 (choice depends on range of motion requirement)
155mm or 215mm MGN7 idler(s)
Single idler or Dual idlers (Single stabilizes in "pitch", Dual also stabilizes in "roll")
Normal or inverted idler(s) (choice depends on intended position of the objective)

Here are some sketches of the various options:
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Picture1_2.JPG
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Picture2_2.JPG

ray_parkhurst
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Re: Idler Rails and Assemblies

Post by ray_parkhurst »

I made an animation of the 18" column, 150mm KR20, 155mm Idler to show how it operates:
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ezgif.com-gif-maker(6).gif

ray_parkhurst
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Re: Idler Rails and Assemblies

Post by ray_parkhurst »

The clamp-type extension systems (like the mjkzz or wemacro solutions) can be mounted to the top plate via arca clamps, giving wide range of movement for the whole system with superb stability.

An alternative is to use bellows which mount on front and rear of the bellows rails, such as the Nikon PB-5, or whose camera and lens standards have mounting holes, such as the Vivitar. I have built a few systems for folks using the Vivitar in this way. The Vivitar is especially nice since it has a very short minimum extension. To enhance this, I had Raf make adapters for M39 and for M40 for enlarger lenses or Tominon lenses, respectively. This allows me to use relatively short focal lengths at minimum magnifications.

ray_parkhurst
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Re: Idler Rails and Assemblies

Post by ray_parkhurst »

Here is a pic of a modified Vivitar bellows with Arca clamps on each standard. This mounts to the top Arca plate shown in my drawings above. You can use this configuration in a few ways:

- Fix the bellows extension and thus magnification, and move the whole bellows along the arca plate for coarse focus, then tighten both clamps
- Clamp the camera standard, then move the lens standard for focusing
- Clamp the lens standard, then move the camera standard for focusing

With both clamps tightened, the automated rail is then used for fine focusing and stacking.

I've found these arrangments to be extremely flexible.

Note that the clamp-type extension systems from mjkzz and wemacro can also mount to arca clamps and mount to the top of the arca plate.
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DSC_4899_2.JPG

ray_parkhurst
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Re: Idler Rails and Assemblies

Post by ray_parkhurst »

I started building one of these assemblies to use myself. Turns out the Pentax Auto Bellows does not play as well with the FF camera as I'd hoped (due to vignetting), so I have converted a Vivitar bellows to E-mount. By removing the T-mount adapter, and milling the adapter mount down to the surface of the camera standard body, I brought the minimum extension of the bellows down to a phenomenal 25mm. Along with the very short E-mount register, I should be able to use very short focal length lenses at much lower magnifications than I could do with the HRT2i on the Pentax bellows.

I chose to go with a 24" column, 150mm KR2001A rail, and dual 215mm idlers with single carriages. I will post pics when it's finished. Unfortunately, I learned I did not have any M2 screws that were long enough for the idler carriages, so they are now on order and due to arrive in about a week.

ray_parkhurst
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Re: Idler Rails and Assemblies

Post by ray_parkhurst »

I've been working with another forum member on an idea to use a motor mount bracket to implement an idler rail system. I have not built this system yet, but here is a concept drawing to show what I'm talking about. This basically turns a THK "A" rail into a "B" rail, but with much longer movement since the idler does not reduce the available movement of the main rail carriage:
KR26 Idler_2.JPG

rjlittlefield
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Re: Idler Rails and Assemblies

Post by rjlittlefield »

I'm looking for some tips about how to get an idler lined up perfectly with another rail.

Background is that I recently experimented with adding an idler to a friend's automated system that had some stability issues. I found it tedious at best to get the idler mounted so as to be perfectly co-linear with the other rail. I was not surprised by that, since "perfectly co-linear" must mean within a few microns, in two dimensions, at a couple of points, after tightening fasteners, else some potentially large forces get built up as the carriages move along their slightly non-aligned tracks.

What are some good ways to do this?

--Rik

ray_parkhurst
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Re: Idler Rails and Assemblies

Post by ray_parkhurst »

Here's the procedure I use:

- Make a dimensional drawing as first-cut for spacings.
- Design to ensure a spacer is required between moving rail/plate and idler carriage
- Build the system to the drawing, except do not install the idler carriage spacer
- Run the moving rail/plate and idler through their extreme excursions
- At both extremes, measure the required spacer thickness
- If needed, add shim to one end of idler rail to equalize the spacers at the extremes
- Install metal spacer with paper shim, sum of thicknesses slightly thicker than required
- Adjust torque on idler carriage screws to bring spacing to required value

This requires that the metal spacer with paper shim be smaller than the carriage. I usually make the spacer to cover only 50% of the carriage (usually 2 of the 4 screws) then make the measurement of thickness on the other 50%.

I'm not sure how perfect the spacing needs to be since I "always" ensure there is plenty of room between the driving carriage and idler. Arca plates and such have some flexibility to compensate some variation in spacings, but the above procedure ensures very close alignment.

Edited to add: I also check side-side colinearity at the extremes and adjust the idler rail to compensate.

rjlittlefield
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Re: Idler Rails and Assemblies

Post by rjlittlefield »

Excellent -- thanks!

--Rik

Darionett
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Re: Idler Rails and Assemblies

Post by Darionett »

this is my contribution of idle rail setup, I hope it can help you.
7256DEC6-ABA6-4B22-A378-C94D516B0C921080.JPG

lothman
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Re: Idler Rails and Assemblies

Post by lothman »

rjlittlefield wrote:
Tue Dec 19, 2023 8:46 pm
What are some good ways to do this?
get a THK type "B" rail with integrated idler like the THK KR2602B

ray_parkhurst
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Re: Idler Rails and Assemblies

Post by ray_parkhurst »

lothman wrote:
Sat Dec 23, 2023 4:18 pm
rjlittlefield wrote:
Tue Dec 19, 2023 8:46 pm
What are some good ways to do this?
get a THK type "B" rail with integrated idler like the THK KR2602B
There is a KR2001B as well. I've built a few systems with the KR2602B and they have worked well. A 120mm Arca clamp fits nicely across the two carriages.

The reason to do a secondary idler rail is if you need a long range of working distances. I've found that the 480mm Arca plates (longest I've been able to find) are excellent for giving a very wide range of movement, allowing me to accommodate a huge range of optical systems. That type of plate can't be driven by a "B" rail since it needs to be supported by an idler much farther away from the driven carriage than the available rails offer. But if you don't need to use a long plate, or if you are able to mount the rail so it can move far enough, then the "B" rails work really well.

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