Author Topic: Domagoj's Potty Mill  (Read 491 times)

Offline Domagoj

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Domagoj's Potty Mill
« on: January 05, 2020, 11:22:58 AM »
It's been more than a week since I introduced myself on this forum, so I suppose it's about time I start actually building something, right?
Like I said in my intro post, I decided on Stewart Hart's Potty Mill engine as my first build (Thank you Mr. Hart for making and providing the plans!). This is going to be a bit of a learning experience for me, since I just recently got a milling machine. I've had a lathe for a bit longer, but by no means I'm an expert, so if you see me doing something wrong, just holler. I'm bound to make mistakes (already did, but more on that in a bit), but hopefully I'll be able to fix them (with your help).

I'm still waiting for some stock to arrive, and considered starting to work on some elements I do have stock for, but I stumbled upon an unexpected find in the workshop. A few pieces of nice 3 mm aluminium plate that just begs to be turned into the base for the engine.

It has a very nice, but fragile brushed finish which I hope to preserve until the engine is complete. It has a protective plastic film, so it's easier to manipulate, but once the film is removed, you can't even look at it wrong or it will scratch, so the film stays for now. It seems to be machinable without tearing too much.
I cut the plate with a hack saw along the lines and cleaned up all the sides in the milling machine, starting with the rough cuts and then cleaning up the factory cut, which seems to be done on large scissors so it's not bad, but could be better. Machined edge certainly looks nicer.

I spot drilled all the mounting holes. DRO was very useful here. (Sidetrack: the milling machine is imperial, and I am thoroughly metric, so installing the DRO was the first thing I did after purchasing the machine. I just can't wrap my mind around it. Of course, during the installation, something got in the way and I installed only X and Y axis, while Z is still pending. I really should do that.)
Anyway, with the DRO and edge finder, this went smoothly. I had to do it in two parts since the vise jaws are a bit too narrow (105 mm) so I had to reposition the plate half way through. Edge find again, check against an earlier spot and drill some more.
After that I drilled 3 mm holes for the engine bits and 5 mm for mounting to the wooden base.

Honestly, I don't know why I decided to go with 5 mm for mounting to the wood, but at that moment 3 mm seemed too small. This could turn out to be my first mistake in this build, but for now I'll go with it, and if it turns out to be problematic I'll figure out the solution later.

While setting up for countersinking the holes (on the bottom side), I had an idea to chamfer the edges of the base plate. A quick try on an offcut looked nice, so I went with it. Thickness of only 3 mm doesn't provide for a very secure workholding when part of it has to stick out, but the procedure was uneventful.

My 4 mm parallels were either too short or too long, so I had to stack some thin ones under them to lift the edge above the vise jaws. It actually worked.


Countersinking the 3 mm holes on the underside:

This tool seems to like slow speeds and a bit of a pressure. It starts to chatter at about 600 RPM, but at 300-400 works nice for such a cheap thing.

And that's it. It took me about two days (couple of hours each day) to get here, but I'm happy I have something done.


Offline propforward

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Re: Domagoj's Potty Mill
« Reply #1 on: January 05, 2020, 12:48:56 PM »
Very nice - looks like you're off to a fine start.
Stuart

Offline Flyboy Jim

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Re: Domagoj's Potty Mill
« Reply #2 on: January 05, 2020, 03:35:23 PM »
Good start.  :ThumbsUp: I'm looking forward to following along.

The use of a shop made Fixture Plate and some shop made clamps might of held your base more securely for machining. I use mine a lot.

Jim
Sherline 4400 Lathe
Sherline 5400 Mill
"You can do small things on big machines, but you can do small things on small machines".

Offline scc

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Re: Domagoj's Potty Mill
« Reply #3 on: January 05, 2020, 04:53:53 PM »
I'm all set too.... :popcorn: :popcorn: :popcorn:           Terry

Offline Admiral_dk

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Re: Domagoj's Potty Mill
« Reply #4 on: January 05, 2020, 07:14:59 PM »
You are off to a good start  :ThumbsUp:

Quote
It starts to chatter at about 600 RPM, but at 300-400 works nice for such a cheap thing.

Back in Tech-School in my youth, we were told to run a countersink tool @ the slowest the drill press would go or between 50 and 200 RPM, but preferably around 90-150 RPM (that was probably in steel). I tried them to do something similar to what you did some months ago, just on plastic - this has to be done at much higher RPM's - but the same happens as you discovered - too low or high RPM's and you get a poor finish with them.

Best wishes

Per

Offline Domagoj

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Re: Domagoj's Potty Mill
« Reply #5 on: January 06, 2020, 08:22:05 AM »
The use of a shop made Fixture Plate and some shop made clamps might of held your base more securely for machining. I use mine a lot.
Yeah, it does look like a useful tool. I'll certainly look into making one. Do you have some pictures of yours?

Back in Tech-School...
I have no formal education when it comes to machining, and I'm learning as I go, so it's no surprise that there are some bits of knowledge that have long since been established, but are new to me.
I am glad that my tool is behaving similar to others, meaning it's not total junk. This being a hobby and all, I usually can't afford expensive tools (even though the few that I do have I absolutely love and recognize their worth) so my usual suppliers are ebay and aliexpress, which unfortunately are not known for stocking highest grade.

Offline Flyboy Jim

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Re: Domagoj's Potty Mill
« Reply #6 on: January 06, 2020, 03:01:26 PM »
The use of a shop made Fixture Plate and some shop made clamps might of held your base more securely for machining. I use mine a lot.
Yeah, it does look like a useful tool. I'll certainly look into making one. Do you have some pictures of yours?

I have a fixture plate for both my mill table and rotary table. Mine were purchased from Sherline for my Sherline mill and RT. If I were doing it again, I would of made mine myself and made both of them bigger. Maybe Chris (Crueby) will be along and post a picture of his. The unpainted clamps I made in my shop.





Here's a fixture plate I made for holding the Flywheels for my P & W build:





Fixture plates and jigs are a whole branch of machining and, being pretty new at machining myself, I've learned a lot about them by looking at the ones others have made. I've found that sometimes making a fixture or jig to hold a part takes a lot more time than machining the part itself.  :thinking:

Jim
Sherline 4400 Lathe
Sherline 5400 Mill
"You can do small things on big machines, but you can do small things on small machines".

Offline crueby

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Re: Domagoj's Potty Mill
« Reply #7 on: January 06, 2020, 06:56:28 PM »
Hi Jim - as requested, here is the tooling plate I had made a couple years ago. This is a bottom view, showing the center button that fits the center hole of the rotary table. There are two rows where it will fit, so I can center the plate or offset it for long parts like con-rods that I want to work on the end of.

And here is a top view of it in use:

Simple to make, made mine from a piece of steel flat stock, aluminum would work too though the holes could wear quicker in that. Drilled a grid of holes for the hold-down clamps, threaded a bunch (and thread more as I need them, it got tiring to do! )
Chris

Offline Domagoj

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Re: Domagoj's Potty Mill
« Reply #8 on: January 06, 2020, 07:11:43 PM »
Those look great.
You guys convinced me, so my To Do list just got a bit longer.

Offline crueby

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Re: Domagoj's Potty Mill
« Reply #9 on: January 06, 2020, 07:18:45 PM »
Tooling plates like that are very handy - when milling down the sides of parts, I stick a bit of card stock, like a 3x5 card piece, under the part so the mill cutter doesn't have to touch the plate and wreck the surface.

Offline Flyboy Jim

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Re: Domagoj's Potty Mill
« Reply #10 on: January 07, 2020, 02:45:36 AM »
Those look great.
You guys convinced me, so my To Do list just got a bit longer.


 :ThumbsUp: :ThumbsUp: :ThumbsUp:

Plus .............shop made fixtures, jigs and tools are really rewarding to make and get used over and over. You won't regret the time spent.

Jim
« Last Edit: January 07, 2020, 02:55:40 AM by Flyboy Jim »
Sherline 4400 Lathe
Sherline 5400 Mill
"You can do small things on big machines, but you can do small things on small machines".

Offline Flyboy Jim

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Re: Domagoj's Potty Mill
« Reply #11 on: January 07, 2020, 02:53:12 AM »
Hi Jim - as requested, here is the tooling plate I had made a couple years ago. This is a bottom view, showing the center button that fits the center hole of the rotary table. There are two rows where it will fit, so I can center the plate or offset it for long parts like con-rods that I want to work on the end of.

Chris.......... your tooling plate for your RT is way more useful than mine for sure. But at least I paid a lot more money for mine!  :facepalm: As you can see from a previous picture, I could barely clamp the Coke Bottle frame to my plate. Your's would of been easy. The moveable Center Button really makes it useful.

Jim
Sherline 4400 Lathe
Sherline 5400 Mill
"You can do small things on big machines, but you can do small things on small machines".

Offline crueby

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Re: Domagoj's Potty Mill
« Reply #12 on: January 07, 2020, 03:20:30 AM »
The rectangular plate is definitely versatile, in some setups I do need the riser block on the head to get it to clear. Also I have the larger mill base with longer table travel.

Offline Domagoj

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Re: Domagoj's Potty Mill
« Reply #13 on: January 09, 2020, 08:16:33 PM »
Some progress on this front. A bit of flat steel stock arrived the other day and I got to work.
The base plate is not particularly exciting, so after that I decided to start on something that actually looks like an engine part - the connecting rod.
It also means I got to use the four jaw chuck, which has been sitting in a drawer unused for quite a while. I just haven't had much opportunity to employ it, so after the chuck change, I quickly (and perhaps a bit inaccurately) chucked up the flat bar. The sides are rounded from rolling and I should have cleaned them up before putting in the lathe. It would have made turning it easier, but that's another lesson learned.

Marked up rough features and started removing the material. Doing interrupted cuts with carbide is probably not the best thing to do, so I went slowly. I did eventually reached the tapered part.

I had some trouble with the carbide insert and the left side where the taper ends and meats the rounded part didn't end up looking all that nice.

The 8 mm hole was drilled, and the small M2.5 threads made.

The rounded end needs some cleaning up. I was thinking of doing it in the milling machine, but just couldn't figure out a safe workholding that would allow me to rotate the part (I don't have a rotary table), so I turned a small aluminum hat/plug/button with an 8 mm and a 12 mm diameters which I used as a guide for grinding.



I did some minor polishing, but I think I'll come back to that. There are still some tool marks that I would like to get rid of as much as possible. I should probably have done more sanding on the tapers while the part was in the lathe, but it's a bit late now. A dremel and a polishing wheel will have to do. I know it's just cosmetic, but this is not a case of function over form, so I think I'll have to do some more polishing.

Offline crueby

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Re: Domagoj's Potty Mill
« Reply #14 on: January 09, 2020, 08:18:59 PM »
Off and running on the parts, nicely done!