POTD- PROJECT OF THE DAY: What Did You Make In Your Shop Today?

piper184 said:
Yes, apologies for the crummy picture. I didn't realize the flash didn't work until I was back in the house.

What I did was bore out some heavy wall pipe for a close fit that let the strut tubes slide inside. Then welded on a butt cap on one end. Turned it all back down to a nice consistent O.D. and drilled and tapped for the threads on the end of the strut. This left enough exposed threads to put a locknut on the outside.

I milled a flat spot on the outside of the tubes so they were easier to clamp and weld. This also got the center lines of the struts closer together. The tubes are 5" long which is the amount of overlap I needed to get everything to fit. It is also sufficient to transfer the twisting forces along a good length of the strut in an effort to keep them from wanting to bend.

The struts are rated at 130# of push with a breakout force of 160# when collapsing. The two struts connected together don't add any force, only travel length. Putting a set on each side doubles the lift to 260# and the breakout force to 320#. I must have gotten that about right because just before the knee starts to come down it gets lose on the dovetails of the column. This is with nothing more than the 6" vise on the table. If I throw the rotary table on too it might be about perfect.
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The floating knee would bother me, I only lock it down for the important jobs. Nice job on the mounting solution!
 
The closest explanation I have seen was a video by This Old Tony:

I think it has more to do with the different surface area of the piston side vs. the rod side of the strut. If it were just sticktion, it would be the same going both ways.

The only information I have is from the McMaster-Carr catalog where it shows the two forces.



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The breakout force is in the threshold valving as a Belleville shim stack valve. Once open, it works against preload pressure. Like speed sensitive valving in shock dampers with a built-in air spring. So when static, you have 160# to overcome initially, and once kinetic you have 130#. The max breakout will never exceed 30# over for struts in series, but they could theoretically sum in parallel at peak. Closing the hatch on your SUV or whatever is still a two finger job because one side always breaks threshold first and the second follows so fast you don't even sense it.
 
pontiac428 said:
The breakout force is in the threshold valving as a Belleville shim stack valve. Once open, it works against preload pressure. Like speed sensitive valving in shock dampers with a built-in air spring. So when static, you have 160# to overcome initially, and once kinetic you have 130#. The max breakout will never exceed 30# over for struts in series, but they could theoretically sum in parallel at peak. Closing the hatch on your SUV or whatever is still a two finger job because one side always breaks threshold first and the second follows so fast you don't even sense it.
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Thank you. That makes sense. I was imagining that the bypasses were orifices with no preloaded "check" valve. I guess that would be just a damper, not a spring.
 
piper184 said:
It just dawned on me that this may be an indication that I need to check the adjustments of the gibs on the knee.
To the Bat-Shop Robbin! We have a mystery to solve!
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Are they fully extended with the knee all the way up, or did you preload them a little?
 
Firstram said:
Are they fully extended with the knee all the way up, or did you preload them a little?
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They are fully extended at the top of the travel, but I was having the chattering at all heights if I let it sit a few minutes between raising and lowering.

I tried to tighten the gibs but they were fairly tight. Then I realized that it was acting just like it did when I would forget to release the knee lock. It was binding!

So then I slacked off the gibs just a little and it works much better now. I did find that if I got them too loose it would have the same effect. After some back and forth the sweet spot was found and it now only does it occasionally. There probably is a little bit of wear in the ways that come into play as well.

My working theory is somewhere in the past the gibs had been snugged up fairly tight. With all the weigh of knee assembly on the lead screw the gibs compensated for any backlash or wear in the lead screw. Now that some of that pressure is off of the lead screw the forces on the dovetails are more balanced and the snug fit was enough to cause the binding.

As for now everything is working very smoothly and I think this "upgrade" will pay dividends in the long run. At least that is the story I am telling my wife. Shhhhh!
 
Put some new front wheels on my welder. The old ones were plastic that was completely rammed full of metal chips and I couldn’t be bothered picking them all out like I did with the rears IMG_5838.jpeg

Also cut 2/3 of the way through a 2” “surprise, I’m stainless!” bar. That was much less fun though
 
As mentioned in an earlier post I haven't gotten much shop time in lately. It's been due largely to old age and the deterioration of my back. In my prime I could easily lift 250 lbs., but more recently 25 lbs. puts a strain on things. To that end I've avoided almost all work in the shop.

I've finally gotten tired of just walking past the machines and dusting or oiling them on occasion. I decided it's time to build a portable crane to lift heavy stock and tooling. I've had and used a 500 lb. and a 1,000 lb. hydraulic table for years. It's now time to convert the smaller one into a base for a crane.

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The crane will then be used to pick up stock, tools, and fixtures to transport them to the appropriate machine. First on the list is to remove a 125 lb. 4 jaw chuck from the lathe and install an 8" one.

This is a work in progress. I've ordered a 2,000 lb. hoist from Amazon. It's identical to the one I put on the trailer except for the fact that it's yellow rather than black. While the 2,000 lb. capacity is far more than I need it's the smallest one I could find with the features I'm looking for. It has to be able to go low enough to pick up heavy items off the floor, go high enough to go over the lathe beds, or mill tables, and extend far enough to lift items off shelves and tables and place them in line with the lathe spindles.

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The boom will be shortened a few inches. and extended and retracted with the use of a linear actuator originally intended for use on a lift chair similar to this.

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The manual winch will be replaced with a 2,500 electric winch I currently have in stock. The winch was originally purchased to be used on the end loader. It only got a few minutes use before I decided it was too small to do the job. It was replaced by one with a 5,000 lb. capacity.

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I'll have to wait to begin the assembly until at least Jan 9th which is supposedly the delivery date of the crane.
 
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