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2/14 Update #2, Bushings

I finished up machining the bushings today, and will take all but 1 to be hardened tomorrow.

I decided to harden them even though I bought the Chromoly tubing. This is because if any of them warp because they’re not hard enough, it will be really tough to remedy, especially if it happens on the 3″ thick upper arm. I’m getting it done for $85 at Certified Metal Craft. I’m going to leave one bushing un-hardened so we can compare and see if hardening is necessary. This will be one of the bushings in the Vertical Supports, as it will be easily accessible and visible. If this bushing does deform, we can remove the Vertical Linkages, and remove the bushing by heating up the surrounding material and pressing the bushing out.

For machining the bushings, I simply machined them to exact length +/- .01, and chamfered the edges. I chamfered them so they won’t have sharp edges, and so the pin will go in easier. It took longer than I expected, as I was having trouble getting them centered on the lathe; they were rotating lopsided, so the faces weren’t parallel. I remedied this by watching the tubing closely as I turned the lathe on, and re-seating it in the chuck if it wasn’t centered.

Tip: When cutting, machine the long piece after each cut. This makes lengths much more accurate when measuring to make the next cut, and also makes machining much easier when you are dealing with the 1″ and 1.5″ long bushings, as you will only need to machine one side when it is short.

It was pretty time consuming to make the bushings, but mostly because I’m still unfamiliar with the lathe. I plan on researching the cost of purchased bushings, as this would save a lot of time vs. machining them. For the big bushings, it costs 138$ to make all of them (53 for steel, 85 for hardening), and a few hours of work. This is still relatively cheap, around $16 for the 3″ long big bushings and $8 for the 1.5″ bushings. I’m going to call a bushing manufacturer to get a price tomorrow and I’ll post it.

It appears I’ve left my camera at the shop again. I’ll update this blog tomorrow with footage of the bushings, and photos.

On the grease channels: grandad said my channels are sufficient.

2/14 Update

I ground the grease channels in the 2.5″ pins yesterday. See the following videos.


I ended up doing one spiral, with a 2″ pitch, and 5 channels running along the length of the pin and rotating slightly. Grease can typically travel about 1/2″ to 3/4″ away from the channels, depending on the clearance between the pin and the bushing. This pattern would distribute it to all except the very centers of the squares, but since the linkages and upper arm will be rotating around the pins, the rotation will cover the rest of the squares.

The channels are the width of the blade of the die grinder, and about 1/16 deep. I may need to make them deeper, as they may clog being this shallow. I’m asking my grandfather today and I’ll update tomorrow.

Update: Grandad said they’ll work. 2/14/12

I also purchased and began machining the bushings. More on that later, I’m heading to the shop.

2/12/12

Slacked off a bit on updating, but hey, it’s the weekend! I HAD to go flying and to a fancy picnic. =)

Anyways, progress has been kinda slow- its not that I was working slowly, it’s that I’m terrible at estimating time. I had a short day Friday as well: ~6 hours.

I’m still working on the 2.5″ pins. Friday, I finished off machining by drilling and tapping the hole thru the center of the pin for the grease fitting. I also drilled the holes which will distribute the grease to the outside of the pins.

The Sharpie you see on the pins is the path I’m going to grind down for the grease to travel through around the pin. It needs to be distributed about the pins’ entire length, to insure it won’t bind with any of the bushings, and that the entire length of the pin will be receiving grease.. I’m debating changing the pattern, as the grease usually can distribute ~1/2″ to 3/4″ away from grease channel, so my channels might be a bit excessive. I also need to make by-passes between the spirals channels in case one channel gets clogged. Designing these channels is a little challenging, as the pin will likely only be rotated about the 15 degrees that the arm rotates at, so more channels are necessary than a fully rotating pin.

Next week, I plan on finishing up the pins as soon as I can get the threaded rod for them. I decided to change it from 1″ course TR to the 1.5″ fine TR. The piranha uses 1.5″, so there must be a good reason for it. I figured the fine thread makes the nut less likely to slip. The 1.5″ will have more holding power at the outside of the pin.

I also started keeping logs in another Google Doc. One for materials purchases, one for materials usage from Enniss, one for time it takes to do each task. The task log will be particularly useful, as it will allow more accurate time estimation for each task. Haven’t filled anything out yet besides purchases.

I received the check yesterday for materials, so no more money hold up.

Here’s a pic for the progress for the week. I received the Half-moons and the blade bushing friday as well. I also purchased the grease fittings from Grainger.