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Old Pharts Duck Under

Mark Kasprowicz
 

I posted a few questions about duck unders on the old group before Christmas. With the advice ringing in my ears I've completed this vertical lifting section using four 28" desk runners. It has counter-weights so it can be stopped at any point between top and bottom, the electrical feed will simply be via hard wiring and I have still to add the 'over the edge' protection which, because I run many locomotives with 'stay alives', cannot simply be a power cut off. But it works and is easy to lift and lower and, best of all, no more scalping. Mark K (BTW to those who have observed that my carpentry is not 5 star I will reply that if I can make it, so can anyone!)
Mark K

Steve Hatch
 

 Ha ha.... I love it Mark.
-Steve

c_bryars@bellsouth.net
 
Edited

Very nice, can you post plans?  Also would it work for multi-deck?

Thanks Cameron

Mark Kasprowicz
 

Cameron

Sorry, I do not have any plans I'm afraid, I just built it up as I went along to fit the space I needed (basically enough height for most and a little post holiday 'girth'). The drawer runners were described as heavy duty and they were certainly heavy. It's crucial to get them perectly vertical or else when the four legs are connected together, the whole thing will lock up when you try to move it. My runners are those which have a soft closing action to the last inch or so the section needs to be lightly pressed home. I first fixed the small edge of the runners to some 1" square wood, then screwed them to the fixed uprights. Finally I added  cross bracing, a peice of ply about 4" deep front to back to keep the whole thing square and the tops for the track. I've yet to source some other weights - at the moment I've about 3lb each side and that will increase slightly as I add scenery. I secured the rope to the bottom of the moving frame and used eyelets not pulleys becuase I wanted a little friction.
You mention Multi layer - do you mean it joins two or more trackbeds at different heights? If so yes, threre are two layers in my version, you can see the second one in the 'lowered' photo. If it helps I can take a few more photos from different angles to help make up for the lack of plans.
Mark

c_bryars@bellsouth.net
 

Greatly appreciated and any more photos would be great.

Cameron

lloyd lehrer
 

I use a double deck slide up that i had made from structural aluminum components. I have a high ceiling so the bridge section has no issues with sliding up high enough, but you could design it so it telescopes both levels one into the other or use two sets of tracks, one for each level, having them slide beside them, one in front of the other. 

On Jan 29, 2018 6:26 AM, "c_bryars@..." <c_bryars@...> wrote:
Very nice, can you post plans?  Also wouls it work for multi-deck?

Thanks Cameron

lloyd lehrer
 

By using the structural alum. Framework and a rectangular sliding frame, i eliminate any lockup since the sliding part keeps it true on the vertical tracks. The slide uses nylon formed glides in matching slots. It holds a tolerance if less than a 1/16".

The parts are made by 80/20 inc.; look up www.8020.net 

On Jan 29, 2018 7:32 AM, "Mark Kasprowicz" <marowicz@...> wrote:
Cameron

Sorry, I do not have any plans I'm afraid, I just built it up as I went along to fit the space I needed (basically enough height for most and a little post holiday 'girth'). The drawer runners were described as heavy duty and they were certainly heavy. It's crucial to get them perectly vertical or else when the four legs are connected together, the whole thing will lock up when you try to move it. My runners are those which have a soft closing action to the last inch or so the section needs to be lightly pressed home. I first fixed the small edge of the runners to some 1" square wood, then screwed them to the fixed uprights. Finally I added  cross bracing, a peice of ply about 4" deep front to back to keep the whole thing square and the tops for the track. I've yet to source some other weights - at the moment I've about 3lb each side and that will increase slightly as I add scenery. I secured the rope to the bottom of the moving frame and used eyelets not pulleys becuase I wanted a little friction.
You mention Multi layer - do you mean it joins two or more trackbeds at different heights? If so yes, threre are two layers in my version, you can see the second one in the 'lowered' photo. If it helps I can take a few more photos from different angles to help make up for the lack of plans.
Mark

Mark Kasprowicz
 

I'd like to see it though I'd be a bit concerned that the use of Aluminium would result in a more fragile structure especially at full extention. My runners are steel and they locate at low level with no error but I will add patern makers dies to ensure a 100% location.

Mark

lloyd lehrer
 

Define full extension. There is none on mine. The vertical rails are rigidly attached to the wall all along the travel of the rigid rectangular slide. Nothing changes as opposed to a drawer slide.

lloyd lehrer 310 951 9097

On Jan 30, 2018 12:15 PM, "Mark Kasprowicz" <marowicz@...> wrote:
I'd like to see it though I'd be a bit concerned that the use of Aluminium would result in a more fragile structure especially at full extention. My runners are steel and they locate at low level with no error but I will add patern makers dies to ensure a 100% location.

Mark

Glenn
 

One way would be to add a slat of wood on each side below the bridge to the bottom of the lift section, It only needs to be as wide as the width of the track.

Minimal would be only at the bottom high enough to block a train, but that would only give protection when lift is fully raised.

Glenn

Mike Conder
 

Mark, I've seen those aluminum (aluminium?) extrusions and they are very thick-walled and stout.  The nylon guides would be the weak link, and they're probably pretty tough (haven't seen those, though.)

Lloyd, in the 1st photo of the third set, what is that wood bar with yellow stripes and a plate bridge?

Mike Conder

Art D3
 
Edited

One of my other pastimes is volunteering as an engineering mentor for a high school robotics team, so I have a fair amount of experience with these extrusions. They are aluminum and they are actually made by several sources 80/20 being one of the originals, Bosch makes a metric version, and several other smaller companies. This is used in industry for making quick and often one off structures like product testing rigs, robotics system, and portable industrial jigs and other structures.

Someone had previously posted about steel being a better choice and stronger than the aluminum. These extruded products are plenty strong especially for building a layout duck under. We have used this product to build a mechanism to lift our 140 pound competition robot over 8' in the air repeatedly.

Aluminum pros - lighter than steel, will not rust, easy to drill and cut (we use an 80 tooth carbide circular saw blade in a chop saw for most cuts), and these extrusions are self - squaring/aligning which helps with getting a smooth running mechanism.
Aluminum cons - pricier than steel or wood construction.

You also mentioned the nylon guide blocks. We've used those too and they are plenty strong for a duck under. If you'd prefer roller bearings, you can purchase V groove bearing that will run in the extrusion tracks as shown below. These are made by a few manufacturers including Bishop Wisecarver.



If you are curious about these types of products, I would recommend looking to some of the competition robotics suppliers out there such as:

http://www.revrobotics.com/rev-25-1238/ The picture above is from the Rev Robotics linear motion products using the extrusion and V groove bearing.
https://www.vexrobotics.com/linear-motion.html Vex has linear motion products that use simple aluminum gussets holding flangeless bearings that roll on aluminum box tubing either 1"x1" or 1"x2" -  0.125" wall thickness which can be found at some Home Depots and Lowes stores.
http://www.andymark.com/product-p/am-3844.htm Andymark has a similar product to the Vex product - gussets holding bearing running on box tubing.

Model railroaders are a resourceful bunch. I'm sure they can adapt one of these products into a bullet-proof duck under.

Art Dutra

lloyd lehrer
 

Mike, those are the shelf plywood pieces holding the track and my safety plate girder "guardwalls" on the bridge.  They just cantilever out from the slider rectangular frame.  This whole assembly is put together with 90 degree inside corner brackets and hex socket head screws. its totally adjustable.  The two nylon slide pieces (the white-ish 1.5" long  by 1/8" parts) are screwed just below the outside corners of each side of the rectangle. They slide in the outer long rails. one rail on each end of the rectangle frame. 

lloyd lehrer, MANHATTAN BEACH, CA (310)951-9097

On Tue, Jan 30, 2018 at 3:35 PM, Mike Conder <vulturenest1@...> wrote:
Mark, I've seen those aluminum (aluminium?) extrusions and they are very thick-walled and stout.  The nylon guides would be the weak link, and they're probably pretty tough (haven't seen those, though.)

Lloyd, in the 1st photo of the third set, what is that wood bar with yellow stripes and a plate bridge?

Mike Conder


Mark Kasprowicz
 
Edited

Point taken about the aluminium - I hadn't thought about extruded section. Even if it had occured to me I would probably still have gone for the drawer runners. I think there is a difference between the two designs - mine is 21" wide and 24" deep so it needed support at the front as well as the back. The draw runners telescope into themselves so there is no visual intrusion when the section is lowered. With four legs and runners it had to be square or it would have locked up. The bridge was an afterthought and may not make it into the final scene. I am growing  keener on a low trestle rather like the Hangman on C&TS.

Anyway that was my way of tackling the problem.

Mark