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And part number and source of the bottom part.

I just happened to have a perfect sized bit of aluminium round stock sitting here (leterally right beside me) and thought I'd drill a quick hole in it a see how it worked real quick.

Hobby store will have this for sure in their round stock selections.

The bottom dogbone end is from their RC car area and can be had in a bag of 10 of them for around 10 bucks I think. I also had it just laying here.

I would appreciate it if you can find the part # for that dogbone part, I have no idea how long to make it and would appreciate it.
My printer assembly is not that far along so I can't measure what it should be as far as length and thread size.

I'll do it if I can, but I had long ago throw out the packaging and sorted these into my bin system here.

I'll have a look and get back to you shortly.

Eaglezsoar wrote:I would appreciate it if you can find the part # for that dogbone part, I have no idea how long to make it and would appreciate it.
My printer assembly is not that far along so I can't measure what it should be as far as length and thread size.

those are actually ball links or tie rod ends. they come in different sizes. the ball links can be popped out like i did to fit 6-32 stock screw.
this one is sized for a 4-40 turnbuckle or screw. They also make a heavy duty version like flateric's Hardware store should stock some 5/16 diameter steel rod to use as the top rod. brb. lol

Hey guys. I have been working on a belt tensioner for a while with the thought of offering them. The challenge is making them cost effective. The ball links are $1-$2 each and you need 6 of them plus the other hardware. I am looking at alternatives and talking to a couple of companies about a large order to get the price down.

Cheers,
Michael

mhackney wrote:Hey guys. I have been working on a belt tensioner for a while with the thought of offering them. The challenge is making them cost effective. The ball links are $1-$2 each and you need 6 of them plus the other hardware. I am looking at alternatives and talking to a couple of companies about a large order to get the price down.

Cheers,
Michael

No hurry, tomorrow will be okay.
Carl

well I made some progress on my idea, I did manage to get some 5/16" diameter steel rod from home depot. I was able to cut it down and drill holes. here is the prototype..
I made a jig to somewhat accurately drill the holes. shown in the photo below, put the rod in the 5/16" hole in the side.
Then drill the smaller holes from the top. Once you drill one of the top smaller holes, put a matching size screw to hold the rod in its place then drill the other hole. That keeps it somewhat lined up. works good.
tomorrow i'll make the rest of the tensioners, almost done with the build.

edit: this idea was not used because I couldn't accurately drill the holes into the rods, even with the makeshift jig i made. I'm currently working a new angle on this. check for it in the following posts

Are those 4-40 screws going into the rod ends?

Eaglezsoar wrote:Are those 4-40 screws going into the rod ends?

yes, i had a bunch of those lying around, but I found some aluminum rod ends i'm going to try out and post and update if it works out.

Instead of a rod end, why not an L-shaped thick sheet metal piece? Mount it upside down, with a hole in each end. The screw for the idler goes through the hole in the top of the L (on the bottom, since it's upside down), and the adjustment screw goes through the base of the L (on the top) into a nylon-insert locknut. That hole is close enough to the bend in the L to keep the locknut from turning while you turn the adjustment screw.

- dan

that would work too. This was just another way. when I first started this was trying to make it out of off the shelf parts that didn't require any machining. I'm still trying to do that. Just trying to find the parts that fit, is the hard part.

if you got ideas share em.

Here's a sketch, if I can attach it right.

- dan

The tension on the L might want to unbend it. Maybe an upside-down U in its place with the locknut in the base of the U (at the top) would work better.

- dan

http://www.mcmaster.com/#corner-brackets/=lyvouc

hmm..mmmm

I think it's important to avoid too much tension on the belts too, as well as having some way to ensure the tension is the same on all three belts. Maybe a coil compression spring between the adjustment screw head and the horizontal rod, so the belt tension would be roughly the same when the springs are compressed the same amount for all three belts.

- dan

I found these searching. Im trying see if can get these fully threaded. the thread on these are 4-40 and the hole is roughly 3mm, so it will fit the stock 6-32 screw, you would just use a nut at the top to tension it. http://store.rc4wd.com/Steely-4-40-Rod- ... p_642.html

I've been toying with the idea of using these with some hollow aluminum tubes in place of the plastic beams and U joints for suspending the hot end platform. Could cause more damage in a crash though.

- dan

dbarrans wrote:I've been toying with the idea of using these with some hollow aluminum tubes in place of the plastic beams and U joints for suspending the hot end platform. Could cause more damage in a crash though.

- dan

saw his on ebay not too long ago..http://www.ebay.com/itm/Reprap-Rostock- ... 4ac1d75198

but that's another project for later maybe.

I have talked to a couple of manufacturers and distributors of the rod ends and some other interesting hardware to try a couple of different ideas for tensioners. I'm looking for metal parts, not nylon or acetal. I think the tension - although not that great - might be an issue with non-metal parts. I am also trying to source off-the-shelf parts to keep machining time (i.e. costs) down. I have the advantage of buying power in that I purchase lots of stuff from these companies so they are always wiling to send me parts to prototype and give volume discounts. I will be posting details, parts used, etc as things start rolling in. I like the simplicity of the cross bar with holes, cap screws through them into the rod ends. Clean, simple and should be easy to source parts and produce.

One of the more promising parts is: Aluminum 6-32 Rod End. I am trying to get these in volume without the steel ball insert. There are a couple of other options too.

As pointed out above, the Rostock builders like these for their delta arms too. Those do require the balls. I've got some of these coming too to experiment with different arm linkages.

cheers,
Michael

Unless a rod end has a nylon insert, you've still got an extra step of loosening or tightening a jam nut when adjusting. Using an L-shaped piece of metal with a locknut doesn't have that problem, and is probably less expensive than the rod end.

- dan

Dan, a simple star lock washer under the cap screw will prevent it from turning too without needing a jam nut or two tools. "Expense" is relative depending on what you are trying to do. I looked at a lot of options including the metal angles and custom fabricated pieces. "L"'s small enough not to look ridiculous are very easy to bend. That would be a bigger problem in my mind. Fabricating something out of thicker stock requires machining and "time is money" as they say. In order to keep the cost of this reasonable, I am trying to source off the shelf parts that can be acquired in quantity at a discount. If it works and I can produce them economically, I will. If not, I'll have tensioners and others can learn from the experience!

alright well, drilling the holes in the top rods wasn't as easy the second time around and thereafter, I just couldn't get the holes accurately centered. so i'm going to continue searching for alternatives.

mhackney, when you have your kits ready, I would get a set.

I'll keep everyone up to date on progress. Just waiting for parts to come in. Ironically, the cross rods are the one component I have completed! They are made of stock on hand on my mill where I can hold it firmly while drilling the holes.