Author Topic: Textile Mill Diorama  (Read 28036 times)

Offline J.L.

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Re: Textile Mill Diorama
« Reply #525 on: August 04, 2018, 08:38:27 PM »
Thanks Chris.

I like the idea of cutting a groove in the eccentric with a sharp parting tool as well. :)

Can I assume then, that the large hole in the strap be could be cut first to set a given diameter for the tracking groove in the eccentric?

Because the strap is bolted together, it could easily be taken apart and straddled around the eccentric (while the eccentric is still in the jaws) for testing the tenon (with side shoulder cuts already anticipated in the strap).

The only problem I see there is that the strap has to be flipped round in the 4-jaw to make these relief cuts if they are not correct the first time. Resettisng a part exactly in the jaws eadh time has never been a strong point for me. 

John

P.S. Thanks Chris for the explanatory labelled picture. It came in while I was typing a reply to your helpful post.
« Last Edit: August 04, 2018, 08:42:14 PM by J.L. »

Offline crueby

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Re: Textile Mill Diorama
« Reply #526 on: August 04, 2018, 09:00:55 PM »
Yup - I usually make the strap first, then the eccentric to fit. You are right about the second side, though if you have a boring bar with a steep angle on the inside edge, you can cut both sides in one chucking, it just leaves a slight angle on one side of the tenon, but so what? It will not be seen, and that way you are sure the holes are all concentric.

Online zeeprogrammer

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Re: Textile Mill Diorama
« Reply #527 on: August 04, 2018, 09:05:53 PM »
Can I assume then, that the large hole in the strap be could be cut first to set a given diameter for the tracking groove in the eccentric?

Because the strap is bolted together, it could easily be taken apart and straddled around the eccentric (while the eccentric is still in the jaws) for testing the tenon (with side shoulder cuts already anticipated in the strap).

That's my thinking. But I'll have a question shortly about the shoulders.

The only problem I see there is that the strap has to be flipped round in the 4-jaw to make these relief cuts if they are not correct the first time. Resettisng a part exactly in the jaws eadh time has never been a strong point for me. 

If the strap is done right then it's the eccentric (edges and/or groove) that gets adjusted to match. If the eccentric is done first (and correctly) then it may not be just the shoulders that need adjusting.

Going back to the shoulders...I've never done one that way (again...very limited experience) so I'm curious as to their advantage and/or need.

...just saw Chris's post...so that kind of addresses my thought on strap first.
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Offline crueby

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Re: Textile Mill Diorama
« Reply #528 on: August 04, 2018, 09:09:25 PM »
If you have the groove narrower than the straps, then you need the shoulders on the strap to form the tenon. The advantage of this method is that the two straps (in a reversing engine) can be butted right up to each other, saving space on the crankshaft. Even if there is only one strap, it saves space. If space is not an issue, then making the groove the width of the strap is a simpler build all the way around.

Online zeeprogrammer

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Re: Textile Mill Diorama
« Reply #529 on: August 04, 2018, 09:18:26 PM »
Even if there is only one strap, it saves space.

I think I understand. There's a minimum thickness to the strap (at least enough for bolts to put it together not to mention the rod it connects).
With shoulders, the eccentric can be the same width.
Without shoulders, the eccentric has to be wider in order to provide the edges.
Thanks.

Apologies to John.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
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Offline J.L.

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Re: Textile Mill Diorama
« Reply #530 on: August 04, 2018, 10:18:28 PM »
No apologies necessary Carl. It's all about learning and sharing.

Here's a scary photo. I set up the strap this way just for the shot. It's not centered at all or has no brass shims under the jaws.

But it does bring up a number of idle thoughts. In a perfect world, this strap would be thinned down on each side of the through bolts on a flat table. But I see no way of clamping it. If it were made of ferrous material, the pros would probably use a magnetic table. I have to shave material off both sides of the strap equally by resetting in the 4-jaw each time?  :-\

Second, the hole has no centre and is oval. :???: They over-compensated for the kerf thickness. It did not close up the casting to a round hole at all.

Third, I've never bored a hole with a boring tool in my life.  ::)

In a perfect world again, the pros probably would come up with a way of using CNC equipment to get a centered hole with concentric shoulder allowances on each side.

Must think about milling equal amount of material off both sides some other way.


Offline wagnmkr

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Re: Textile Mill Diorama
« Reply #531 on: August 04, 2018, 10:36:47 PM »
John, I would say you have it just about right. Put some flat packing up against the chuck, behind you piece. Double sided tap will hold the packing in. Center two opposite sides of the opening at a time. (The long part of the oval and then the short sides of the oval.)

Just take a very light skim of one side, just enough to get a good surface. Then flip it around and do the other side to size.

That is how I have done it before.

I am going to be in your neck of the woods on Monday morning if you would like some help.

Tom

Tom
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Offline J.L.

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Re: Textile Mill Diorama
« Reply #532 on: August 04, 2018, 10:57:05 PM »
Monday sound great Tom.

Thanks for the support. But have a look at this photo. I got thinking about having the strap sit flat so that equal amounts of material could be cut from each side.

Also, I've heard of some kind of fly cutters that spin to cut holes. A possibility, but your idea of packing and boring with a boring tool may be better.

I'll go ahead and bring the straps to 5/16"; 3/16" for the track and 1/6" for the flange on each side.

John


Offline wagnmkr

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Re: Textile Mill Diorama
« Reply #533 on: August 05, 2018, 01:37:49 AM »
That will work for the thickness John.

All that you need for boring the inside diameter is a regular cutting tool that is ground for left hand cutting. That can be mounted in the tool post like a boring bar. The bar works as well. I have a strong one if you need it.

10am Monday?

Tom
I was cut out to be rich ... but ... I was sown up all wrong!

Offline J.L.

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Re: Textile Mill Diorama
« Reply #534 on: August 09, 2018, 12:44:16 PM »
Tom, thank you for a wonderful visit. Your help in suggesting how to proceed with the straps and eccentrics was very much a ppreciated.

Here are some photos of the first strap finished. I have a story to tell about the second one, but here are some shots showing my first boring attempt at making a strap.

The bore is 1 1/4"; the shoulder 1 3/8". In the first shot, the strap has been turned around in the chuck so that the second side can be faced and shouldered. Getting the part zeroed in was important to get the shoulder concentric with the already bored hole.




Offline J.L.

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Customer Service
« Reply #535 on: August 09, 2018, 01:09:16 PM »
The pictures above show the second strap. I was not so lucky with the first one. I felt very proud of myself after completing the boring and shouldering of the first one. The only thing left to do was drill an angled hole for the oil hole in the back of the strap.

You gueseed it. Half way through, the drill snapped! Game over. The part was ruined.   :-[

I fussed and fussed trying to come up with some way of saving that part. No go. I went upstairs and sent an email to the company where I bought the castings in Bathurst, New South Wales, Australia explaining the situation. This would be yesterday afternoon.

This morning I received a very nice email from sales at E & J Winter - Bolton Scale Models. The part will be replaced free of charge. I want to use the name of the kind gentleman whol sent me this most accommodating email, but have not had an opportunity to ask permission to use his name on this forum.  He should be recognized.

We read of displeasure with some scale model companies specializing in cast kits for engines, but here is an example of exemplary, quick  customer service.

BTW
Instead of an angled oil hole, which does look a little raw, a vertical hole was drilled and tapped for an oil cup on the second strap. Then a cross hole was drilled in from the back and angled down slightly to enter the raceway.  It was plugged with a very short cosmetic brass piece of round rod. Care was taken to make sure that little piece did not interfere with the oil flow from the cup above.

John




Offline b.lindsey

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Re: Textile Mill Diorama
« Reply #536 on: August 09, 2018, 04:20:00 PM »
The strap looks very nice John. It's always nice to find suppliers that are so accommodating too, and we need to recognize them.

Bill

Offline J.L.

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Machining the Eccentric
« Reply #537 on: August 09, 2018, 08:01:26 PM »
Thanks Bill.
Right on. That will happen.

There are so many ways of arriving at the same point, but I am going to go about making this eccentric a way that makes sense to me. The construction notes suggest moving the eccentric its offset distance (3/16") first to drill and ream the axle hole. In these photos, you can quickly see dead centre. Offsetting would be very easy to do at this stage.

But then a stub mandrel would have to be made to hold the eccentric with a bolt. The stub mandrel would be offset after making. That sounds to me to be a lot of extra work and hints at errors in concentricity. It is mentioned that a friction fit would be required as well as the bolt and that if the eccentric slips on the mandrel, Loctite could be used. Hmm.....

I plan to leave the eccentric alone as you see it here and machine the outside of the eccentric's rim with track and shoulders. Then, the part will be offset for drilling.

The only donwside I see here is that all the waste material at the back of the eccentric will have to be carefuly removed to keep the front and back faces parallel.

At least that's the plan.  :)

Edit:
I guess a stub mandral would make it easier to remove all that waste material on the backside. Also, you wouldn't have to grip or perhaps mar the eccentric's rim.
« Last Edit: August 09, 2018, 08:45:20 PM by J.L. »

Offline BAH

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Textile Mill Diorama
« Reply #538 on: August 10, 2018, 03:32:48 AM »
I broke a tap in a brass casting a couple of years ago. I soaked the part in a Alum-water mix then sat it on top of one of those candle warmer plates. Three days later, the tap was a fine sludge.

Offline J.L.

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Re: Textile Mill Diorama
« Reply #539 on: August 11, 2018, 06:12:43 PM »
Interesting.

I created a situation for myself by chucking the eccentric by its little cast stub.

Now that the track has been cut, it's time to offset the eccentric. But I suspect that the little stub will not move laterally properly or may even foul the vertical jaws. And of course it could tip in the precess and begin to wobble.

I decided to remove the 4-jaw and not move the eccentric at all but use the milling table instead.  You can see the offset in the second and third picture.
 The offset is 5/32" for this smaller eccentric.

It looks as though I'm going to be using a stub mandrel to finish this project after all.