Another Rupnow 1 by 1

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Brian Rupnow

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Very glad that I see you continuing with the build.---This build isn't for sissies. You will learn to figure out a few things before you are done here.---Brian
 

Eccentric

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Looking great. I think making the crankshaft is one of the most challenging, most rewarding and most nerve wracking parts of the build. I hate to admit it, but I rarely get my crank right on the first try, hopefully you will best me in this regard. But I learn something everytime and I am getting better and learning little tricks. Patience is the key.

I agree with you and don't think the homemade aluminum lathe dog is going to hold up, you have a lot of turning ahead of you. I recommend this set: Lathe Dog Set | Lathe Dogs for Sale | LittleMachineShop

They are only 35 bucks and have a whole progression of sizes that you will use as you turn down the crankshaft. They are steel and will allow you to really crank down on the hold down bolt. You can see an example in the last picture of this series.


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I use this type of small carbide cutter to turn down the sides of the crank web. Like you I use the mill to remove the material and cut the slot to size, but there is one last cut the mill cannot do. And I use

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this type of homemade HSS cutter for the crankpin. It is relieved on the sides and has the forked snake tongue shape on the end to reduce the amount of the cutter actually in contact with the work piece. I crank it in a couple of thou and then move the cutter back and forth. As I approach the target dimension, I run my lathe slow, like 250 RPM to eliminate the chatter. This is the most nerve wracking part for me, as I approach the actual dimension, you over shoot and the part is ruined. I turn to about .0015" over then use files, stones and emery paper to finish to size.

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Here is a collection of tools used to bring the crankpin to final dimension and polish. It is important to be cognizant of the pressure used across the pin, you don't want to make one side of the pin smaller than the other. That is a problem with files for example, if you press evenly then move it back and forth, the middle of the pin is in contact with the file more than the edges and you get a low spot in the middle. I use the calipers and micrometer constantly throughout the process. I use strips of emery paper for the final finish.

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If it is available, I use the connecting rod to test fit. I am careful not to over tighten the cap before the pin is to dimension, but this proves that the web dimension is good and the final fit is good.

You can see the lathe dog in this picture. Also the reason my steel is black is that I stress relieve the blank in the heat treat oven and let it oven cool overnight. Don't know how much this helps.

Keep up the great work.
 

CFLBob

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Thanks for that excellent discussion. Lots of good points to come back to again.

This one really resonated
That is a problem with files for example, if you press evenly then move it back and forth, the middle of the pin is in contact with the file more than the edges and you get a low spot in the middle.
I think I've been there on different tasks.

My immediate problem is that I have two sets of cutters, one 1/4" shank set for the Sherline lathes and one 3/8" shank set for this big lathe, the Little Machine Shop 3540 (a SIEG SC4). The L & R cutters are wider than the opening in the bar that I roughed out on the mill. I used a flat ended cutter similar to the one you show except with no cutout that happened to fit. I need to open the slot close to final width with either the square tip or something. I'm thinking of using one of the 1/4" cutters.
ChatterMarks.jpg

I hadn't noticed the chatter until this picture.

Your lathe looks so much like my LMS lathe that it's spooky.
 

CFLBob

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Well, it has been almost two weeks since the last update and not much to say. I concluded my shop-made dog wasn't going to work and after exchanging emails with Little Machine Shop about using the chuck mounting plate instead, I ordered a face plate for my lathe and their two biggest lathe dogs. For smaller pieces, I have the equivalent tools for my Sherline, but I've never used them in the 15+ years I've had them.

Let me note first that the people who make these accessories never include instruction sheets. I think their view is that if you're using a lathe you should be professionally trained and you should know how to maintain or upgrade it. I also wouldn't be surprised if not including instructions might have some aspect of trying to protect themselves from spurious lawsuits.

Now, I'm fully self-trained, I take responsibility for myself, and there really didn't seem like many ways to put it on incorrectly. It has three bolt holes on the back which match with three through holes on the mounting plate that's standard on the lathe. I put the first bolt in, went to rotate the two plates to put in the next bolt and quickly found the combination wouldn't turn. There was interference between a different bolt on the lathe and the faceplate.

FacePlateCollision.jpg


That bolt (M8?) has two nuts on it, putting that spring under tension. It sticks maybe 1/8" inch into that cavity in the casting. The bent, black sheet metal you see on the left and top edges is holding a clear plastic "lathe chuck guard" that is supposed to keep your fingers away from the chuck but primarily seems to catch oil the chuck may sling. A closer look showed that when the guard is down, the faceplate will rub on the plastic and I'm sure eventually (a few minutes) will wear through it. A note on the faceplate's product page says, “This faceplate will not fit with the plastic chuck guard in place.”

I'm going to gloss over me looking at the lathe and trying to figure out how to remove that for several hours when the answer is visible right there in that picture. All I had to do was unscrew the two nuts on the right end of the interfering bolt and then the cover just slides off the bolt, Once that's done, just unscrew that bolt. That's when I set things up to hurt myself.

FacePlate_w_Dog_bar.jpg


This is the faceplate, lathe dog, crankcase blank and all.

You can see above that I'm using a parting tool to shave that side of the cutout, and to minimize how much tool was exposed, cranked the cross slide and QCTP forward. It's like this.

Along_Bar.jpg


I'm not completely sure how it happened, but I think I put my right hand on top of the tool holder and let my finger stick out forward a little too far while getting started. The bar was spinning and it whacked my finger. It tore the end of my finger off breaking almost all of the fingernail, but it stayed attached by a lot of skin. We figured it was time to go to an urgent care place. The doctor there said the end segment of bone in that finger was broken and they don't treat "open fractures." They told me to go to an ER. Where I sat for 3-1/2 hours, never talked to or saw a doctor, never really had anyone look at it closely, then had a nurse leave the blood soaked and hardened gauze pad from the Urgent Care place on the finger, wrap some self-adhesive gauze around it, and refer me to a hand surgeon. This was last Monday the 13th.

Long story shortened, the surgeon got me into the office Wednesday and did the surgery the day after that. This is called a degloving injury but do yourself a favor and don't look for example images. I will still have 10 full-length fingers, and might even have 10 fingernails. I mean, I do now, but part of the fix was to sew the half or 2/3 of nail that broke off back onto the nail bed and it's going to take months to see how that grows.

I just took off the oversized bandage I've been wearing since Thursday and switched to something smaller. It's likely to be another week before I can get any more work done.

I need to order some more metal, so this is a good time to pay attention to those things.
 

Brian Rupnow

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Bob---Sorry you hurt yourself. I've had a few whacks from the chuck, but nothing hospital worthy. I'm not exactly afraid of my machines, but I treat them with a great deal of respect.
 

CFLBob

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Bob---Sorry you hurt yourself. I've had a few whacks from the chuck, but nothing hospital worthy. I'm not exactly afraid of my machines, but I treat them with a great deal of respect.
This is the first time I've ever needed anything beyond a plain old band-aid from anything in 40+ years of wood and metal working It obviously could have been much worse, but it was just from a moment of inattention.

The previous week, I was telling someone to watch out because anything that cuts metal isn't going to get slowed down by skin and bone. Anytime we're using any machine, something bad could happen.
 

Eccentric

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Bob,

I am also sorry you got hurt, I hope everything heals OK. The name of the injury , degloving, gives me the creeps and shivers. Sorry it had to be you, but a little reminder now and then of how dangerous our machines can be is not a bad thing. I'll continue to be extra vigilant in your name.

I've always had mixed feeling about those "chuck guards" on the smaller hobby lathes. Do they give a false sense of security? Do they enable people to be lax respecting the moving chuck? Are they a neccessity for the beginning hobbiest? We all are aware of the chuck and work close to it, especially with files (which always have a nice fat handle so it won't be driven through the palm of our hand by accident, right?).

Take care of yourself and I hope to see you back in the workshop soon. Your crank is coming along nicely.

Greg
 

CFLBob

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Thanks, Greg. I've found over the last two days that I forget to use the pain meds, which clearly means I don't need them. That's a good sign. The finger is still a bit swollen and the range of motion isn't back but it's coming back.

My followup visit with the surgeon is Friday morning and I'm hoping to be back to more or less normal. I don't know if that's even possible, if I'll get another 10 day followup or what, but 10 days to two weeks is about when they take out regular stitches. That's ignoring the 6 months for the nail to grow back out.

Meanwhile, I've been rounding up the metal stock I need but didn't pick up when I was starting because it seemed like the sizes I could buy were absurd compared to what I need. Like I need about 1" length of a O-1 tool steel to make the cam, and the smallest bars I could find were 36" (that 1" I quote is over twice the finished length of the cam).

I think I'm about to order a flywheel casting from Martin Models instead of doing the built up flywheel Brian did in the original.
 

Brian Rupnow

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Bob--In my opinion, no one should feel bad about buying a flywheel , a sparkplug, or a carburetor. I think everyone should build one of the above mentioned things once, just to prove to themselves that they can. Then, having proved to yourself and the world that you have actually made these things and that they are in the range of your capabilities, go ahead and buy them.---Brian
 
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