Gallery, Projects and General > How do I??

How square is it? And or Where do you start?

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SPiN Racing:
Heya guys.

This is a theory type question.. and I think since a lot of you have experience making that first cut on something.. more times than I can imagine.. I figure I will ask.

THe castings, for the coke bottle engines, as well as the various parts has prompted me with a question.

Where do you start?

An example.. the casting for some sort of cover in one of the bottle threads. (Im posting here so it doesnt muddle the specific thread)

Its square... roughly. No side is true. Is it PERFECTLY square? I highly doubt it.
THe protruding square, isnt true/square either.
Is it exactly centered over the bottom one? I doubt that as well.
(This is the part Im specifically thinking of.)


So... the bottom isnt flat.
The sides are not flat
No specific surface is accurate to use as a reference.

So this being the case.. How do you chuck that bad boy into the lathe to cut the bottom flat.. and be accurate?
Guess?

And more accurately....
How do you mill a side on it.. that is square to the bulk of the item?


I suppose what I would do Is simply chuck it in the lathe as close to what I could guess to be accurate.. and face it.
Then flip it over, and chuck it again with the now "flat Surface" against the face of the chuck, and then face it again to make them parallel.

But then how do you make a side flat?

Put it into a vice in the mill and do a best guess for the first side?
Then simple use that as your reference surface that all are oriented from?



I dont mean to sound completely lost. I make do with my parts, and will come up with a method for making it as square and true as I can think of.. But I imagine its like the... (mental blank) chuck plate. I got one with my lathe.. but until I was here never knew what it was for. Now its slowly cooking in the back of my brain as another option for turning things...

So what is the "preferred" method for squaring and facing all the sides on an item like that? Or is it like so many things... 20 different ways to achieve the same result?

bogstandard:
Spin,

A few questions.

Are there any faces you want to leave in a rough finish? Some people like to have the casting finish showing in certain places.

Which is the critical fit square? The large or small, or both?

Do you have to reduce the thickness any?

Just to assist, you say you have a mill, do you have parallels as well, and has the vice fixed jaw been trammed to run perfectly parallel to the table, or do you want to do it on the lathe?

There are many ways to do the job, it all depends what you've got and what you need to achieve. :smart:

Good this machining lark, isn't it?  :D :D

Bogs

sbwhart:
Hi Spin

First thing to do with a casting is to clean any flash of it and to run a rule over to check where the meat of the material is and that you can get what you want out of it.

Squaring up in the lathe. with a four jaw

1:- Roughly find the centre by marking across the diagonals, set this up in the four jaw it dosn't realy mater which side you do first, and face it off flat.

2:- Turn it over and do the second side push it hard up against the back face of the chuck or if it sits to far back, push it up against a parallel DONT FORGET TO REMOVE PARALLEL BEFORE YOU START THE MACHINE UP. skim up second side, I find it pays not to bring it to size at this stage leave some meat on and bring it to size with a second set up.

3:- In four jaw skim up an edge, turn it round and using the parallel trick skim up second edge. this gives you two parallel edges

4:- Getting edges square can be a bit more tricky, what I'd do is bring them roughly square with a file and then set them up in four jaw and skim them as for first two sides if you lucky they will come out square if not you may have to pack them out in the chuck, with paper or bear can shim.

5:- When you've got it square you can mark out set up again and bring to size.

6:- Little top square best way if you don't have a mill is to file it.

That's the long winded way

Quick way if you'v got a mill:-

Kit:- End mill or fly cutter, Machine Vice, Dial Test Indicator for setting up vice, Parallels, Set Square.

1:- Get the faces flat and parallel in the lathe four jaw this is far quicker than trying to do it in the mill (I've found) but you could do it in the mill if you want

2:- First check that your vice is set up square  (Tram the jaws with a clock)

3:- In the vice Skim up one edge, Set this edge flat on a parallel in the vice. Tip old ball races make good parallels broken down and sliced up into handy lengths with a dremil. :thumbup:

4:- To get edges square this is where traming the vice helps, this time set the work up so that it edge sticks out of the side of the vice, and skim it up using the side of the mill cutter, if the vice is square, it should come out spot on. The final edge is easy by again setting the good edge on a parallel

5:- Mark it out and bring to size.

6:- When you got the outside square the little square on the top should be easy.

If you don't fancy any of these ways you could do it as our Great Grandfather did with a file and a square, it'll take longer:- but hay this is a hobby  :headbang:

Hope this helps
 :wave:
Stew

sbwhart:
Hi Chaps

You may find this site usful http://mokei-jouki.hp.infoseek.co.jp/e-Wiltop.htm

I think I may have posted before:- but hay, who's counting.

This chap has some real interesting set ups and jigs. I've copied or adopted some of his method for my project.
read it through I'm shure you'l find it of use if not now but in the future.

Have :wave:

fun

Stew

Bernd:
SPiN,

Both Bog's and Stew explained the how to's pretty good.

I'll add to this by saying. The part is almost a presion casting, meaning that it is quite accurate. All castings are made over size to a certain extent so you have material to remove to make it suqare, round or what ever. If the casting is a bad one with very little excess stock to remove then it becomes a bit harder.

The first thing you need to do on a casting this small is remove all casting flash (bumps of metal) so that it sits flat. Since it was a square casting I chose the milling machine. It would be hard to hold in a four jaw chuck. If you go to my coke bottle thread and look at the second picture of the mill you'll notice I have the part held down on the mill table and against a back stop. This is about as square as I could get it. Then I used a clamp to hold the casting to the table. Next I used an end mill to just barely clean up the top part. This left me with three sides of the part just cleaned up. In other words I was roughing out the part and not taking it to final finish. It's hard to see in the picture but the next pic shows the top sides of the part just cleaned up.

By milling the three sides I have made the top part square through the moves of the milling machine. So now I've established square surfaces and parallel surfaces through that first action of milling.

I then was able to use those surfaces to clamp the part in a vise and establish square corners on the rest of the part. Notice in the one shot where I have the lines drawn on the bottom of the part, See how much I needed to remove to get to an overall dimension of .531" .

At the end of that post is the rough part and the semi-finished part. Castings are usaully done in two maching operations. A rough machining operation and then a finish maching operation. This does not always hold true though since it depends on the casting and what needs to be machined on it.

In my next post on the coke bottle engine I will show how I did a round part that was cast. It'll be a while until I get to that. Just keep an eye out for the post.

More questions? Fire away.  :wave:

Bernd

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