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

[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.

Good this machining lark, isn't it? 

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.

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 

Hope this helps
 
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

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. 

Bernd

[SPiN Racing]

WOW very nice posts.

Im happy to see a ton of that sounds exactly like what I have been doing.

Only thing I think Im really missing.. is the parallels. I am now seeing them in Pics.. now that I know what they are.. and what they are FOR... I think Im gonna have to buy a set.

I have a HUGE honking great brigdeport Vise that I have bolted down to the mill table.. and the head is trammed to the table.. but Im gonna go out in the garage and verify that the head and vice are parallel.
Using the vice with parallels is so simple. I never thought of it. I have been putting things in the vice and spending tons of time getting them square by hand. A complete bear. (Loosen, adjust SLIGHTLY...tighten.. measure... loosen.. adjust slightly.. tighten... measure... Loosen.. adjust too far.. cuss.. start over.

The lathe solution I ahve done on several occations.. just put it as close as I can.. face it.. then flip it and repeat.

I think Im also going to have to get a machinists square. Something so simple I dont have in small size. Mine is a carpenters square. /duck


OK been working and in the house all weekend.. time to go make metal shavings fly LOL


Scott

[Bernd]

Scott,

Stew has done a nice job of describing machining a simular part as I did. Here's the link to that thread.
http://madmodder.net/index.php?topic=547.45

Both called slide valves. These are simular to the function of a valve in an internal combustion engine. But one valve will take care of both exhust and intake.

I bet your going to ask how they work. I'll see if I can find a link for you to look at.

Now about those parallels you just discovered. Here's is a pic of a set I was given.


They range in size form 1/2" to 1 5/8". I can't remember if it was here or the HMEM forum were somebody asked if they made metric sizes. Believe it or not they are also makered in meteric. 12MM for the 1/2" and 41mm for the 1 5/8" one. There are 10 sets of parallels in this set or 20 all together. They are/were made by Brown & Sharpe.

I think if I ever was to replace these with the exact same set it would cost me dearly.

Questions? 

Bernd

[Rog02]

Bernd:

I have a couple of those sets except mine are old enough to be in the wood box.  I would hate to think what B&S wants for them these days.  Mine were a dumpster find when a major appliance manufacturer shut down their operation here and shipped all the jobs overseas.  They tossed all the tool room stuff in the dumpsters which in turn was scavenged by the few remaining plant maintenance guys that were closing down the plant. 

Spin:
An old trick is to use a rubber band to hold the parallels in position against the vise jaws.  The band just keeps the parallel from slipping cock-eyed as the vise is closed.  Once the vice is trammed correctly in all three axis and the parallels are in place all you have to do is snug the work in the vice and tap it down with a "thumper".  Check after final tightening all is good.  Cuts down set up time by a bunch and the repeatability is good.   

Another trick is to make some of your own "Sacrificial" parallels from aluminum.  Pretty simple job actually, just clamp a couple of strips of aluminum in the vice and make a square pass on one edge, then flip the strips over and make a parallel cut on the other side with the strips resting on the vice bottom.  The aluminum will not destroy you mills should you crash into them and if you do you haven't destroyed a expensive parallel.  The accuracy is good enough for most daily jobs and you can always drag out the good stuff for those space shuttle parts.

[bogstandard]

Scott,

I grieves me to hear how you are struggling with a lack of basic items, it is a shame you don't live in the UK, I could most probably have kitted you out with my end of year clearouts.

Things like square toolsteel for use on the lathe can be used as basic parallels, as can the larger ranges of ball races, just need a matched pair, one for each end of the part in the vice. Almost anything of reasonable accuracy can be used in the early stages of machining. Later, when you want to get more tighter tolerances and with gained experience you will then know exactly what sort and size of parallels you require.

I tend to buy the cheaper chinese variety, and they do me well for my methods of machining, they may not be as accurate as some very expensive sets you see, but 0.0002" is close enough for me. I also have the advantage I can grind the surfaces of mine to get them perfect if needs be, but only very rarely does that have to be done.

If you get your vice fixed jaw running perfectly parallel to the head, and the base inside the jaws totally level (by using shims under the vice), then with a decent lump to use as a parallel, you will start to get good and repeatable parts.
I did a write up on this site which explains everything I did to true up my mill. Some of it might or might not be relevent to your setup, but the bit on the vice and the follow up posts by other people should get you on the straight and narrow. They mention about soft jaws etc.

http://www.homemodelenginemachinist.com/index.php?topic=2641.0

Bogs

[SPiN Racing]

Thanks guys.

I do appereciate it.

I was out there tonight milling on this lump of aluminum that is really odd. Its in a stair shape, with tapped holes for AN fittings. It mounts to a frame rail in a curved section under the car.

It was a real bear trying to do some basic milling with the vice only.
I didnt want to kick the head over in a 45 degree angle to make a cut along the edge of the part. It doesnt make sense to spend 20 minutes kicking the head to the side.. just to make a 30 second cut that doesnt matter much.. and then 30 minutes getting the head square again.

I am getting there slowly.
As we all know.. money is tight.. so I get tools a little at a time.

parallels and a square are the next purchase... Oh and a draw bar. I wondered why the draw bar was tight. It would spin freely, then a snug of it like a friend the machinist/hacker (I now realise) said to do.. and when taking it off.. sometimes it was tough to undo. SOOO I pulled it out.. adn the threads are all galled up, and appear stretched. SOmeone laid into the thing at some point I thnik.. and must have really messed them up. ALso the top of the nut(?) is all mushroomed over. SO its time to replace it... I think they are 19 bucks from Wholesale Tool.


The only machinists I know.. one owns a CNC machine shop that went away.. and he HATES manual machines.
The other one has some really old machines that are really nice. One is a HUGE honking Mauser.. I think it has like 24 or 36" swing.. or.. wait.. The chuck is HUGE. I think thats the 24 or 36 part. He can turn rims on it.

He is.. very very smart. I mean. He is likely the smartest person I have ever met. (Father is a retired Colonel.. so I have met some theoretically smart people). Thing is.. he is soooooo intelligent that he cant even LOOK at something without smashing the whole concept to ashes.

FOr example.. Lets say I need to machine an adapter for a transmission to a different engine.
He would not say.. Oh yes.. do A B C X Y Z.... he would say that an adapter is crap.. and you ened to make a bellhousing from scratch.. But realistically the whole transmission idea is junk. What you neeed to do is make a Constant Velocity transmission to replace it. Because the regular transmission is too inefficient. And then start grabbing parts and paper to draw it up. And will not ever ever ever... help with the adapter.

I told him about the ball turner.. and he went on for 30 minutes how it wont work, and is horribly inefficient.  Of course many many of us already know the design works fine.


SO yes.

I read the posts here.. and put them in my brain and let them percolate.

I actually made a cup from pink plastic tonight, before dinner, using my boring bars. Had some left over bushing material.. so I spun it up and gave it to my wife. She gave me the eyebrow.. and then said.. Thats nice honey. /shrug
Hadnt used them yet, so wanted to see how things go. Now I know

[Stilldrillin]

I used to make some of the simplest, most effective parallels from steel banding strip.

Two pieces of steel strip, both curved into a shallow S shape, to stand on edge.

Instant, cheap, disposable parallels..... 

[sbwhart]

[Both called slide valves. These are simular to the function of a valve in an internal combustion engine. But one valve will take care of both exhust and intake.

I bet your going to ask how they work. I'll see if I can find a link for you to look at.


Hi Chaps

Found this link explaining how a slide valve works, tried to do it myselve but got bogged down 

http://www.mgsteam.btinternet.co.uk/svalve.htm

The lap and lead symilar to advance and retard on an IC engine, it gives you a bit of leway when making a valve, as long as your just going to run the engine on air you can get away with quite a bit of error, I messed arround with the timing of my Beam engine I was suprized at how far I could be out and for the engine to still run.

Have fun

 
Stew

[Bernd]

Great link find there Stew. That should explain it far better than words.

Bernd