How do I - locate centre and position end mill? - basic milling.

[raynerd]

Hi Guys

I`m after some real real basic milling advice before I make a start. If anyone could suggest a book, website or such that I could learn this, to you, obvious skills, then please do post up.

1. Say I wanted to make the part shown here at the back - partly hidden by the motor. It looks like a simple flat piece -



So I have the plans and if I am being honest, I bet I could have a good go, but I don`t think I would be doing it correctly! So lets consider we have the correct height of material, so it is a case of cutting to shape, and then trueing the edges. Would it be a simple case of taking a sheet, cutting it to rough shape with a hand saw and then mounting it in the vice to true the edges? But with such a big piece how would you hold it in the vice, what orientation? Also, to true the edges of the piece would you hold it vertically so that you were cutting with the end of the end mill or some how overhanging the piece and running the side of end-mill down the sides?


2. Basically if I want to mill a slot as shown below:



What would be the correct way to "locate" the end mill to position. If I used a slightly smaller end mill, I could produce the slot and then widen it to the correct size - would this be OK?  How could I get it accurate if I was using the correct size endmill, so I would need it bang on first time?

Sorry, I know they are the basics but I want to do it correctly.
 

[bogstandard]

Chris,

You are asking for a lot of info in one post. You could write twenty pages and still not show how to square up an edge correctly.

The basics are, first get the job held securely and in the correct position to carry out the work. You will have to know your materials, so that you can select the right cutter for the job and the correct cutting lubricant to use. You will need to know what each type of cutter is used for, and how that cutter is set up to do the job. Feeds and speeds and recognising the way the cutter is doing it's job, and the list goes on and on.

You need to get the basics under your belt first, otherwise you could easily have a permanent impression of a tool or piece part in the middle of your forehead. The milling machine is one of the most dangerous machines for a model engineer to work with. The first thing you have to do is gain respect for the machine before you even turn it on.

I put up some links previously that will give you the basic insight into how and why and what if's of machining.

http://madmodder.net/index.php?topic=535.0

http://madmodder.net/index.php?topic=944.0

There are many more sites like these that can give you the basic information to get you started.

With regards to your question about making slots. The flex on a cutter will almost guarantee that it will cut oversized or very roughly if you just go straight in as you show. You would need to relieve the cutter pressure by either drilling away excess material, or remove it with a smaller cutter first. Then using the correct sized cutter to bring it to final size, even then it can sometimes cut oversized. I sometimes use a one sized down cutter and bring it out to correct width using that, but your end radius will be incorrect, so you either have to accept it as it is, or use the correct sized cutter to bring that part to size. That is on my very rigid machine, on yours, it is even more critical that you get the cutter pressures down.

More to it than you think isn't there Chris?, and you will find every job is different in the way it is handled. Reading about it can only take you so far, it is the hands on experience that gets good results.

I know this is a very negative post of mine, but you have to remember that you will be doing these jobs on your own, and away from other people. So god forbid, if something nasty does happen, you might not be found for hours. So unless you can get yourself to a stage where you can safely work by yourself with such a dangerous machine, you have to take things very steady and gradually. You might get away with it for a while, on the other hand, it could bite you the first time you use it, but bite you it will, eventually, unless of course you can walk on water.

John

[Darren]

Some good advice there from John,

Chris,
I'm new to milling as well, that is why I recently undertook a mundane task of making those T-nuts. My first time with steel.
I learnt a awful lot making these. My point is, make something simple to start with, take it slow, keep the speeds slow and work your way up.

Above all take tiny cuts, don't try to sink the cutter in and do it all in one pass.

But listen to the machine, it will talk to you.....

[raynerd]

I appreciate everything you have said regarding safety. I have had the machine over a week now and I only turned it on for one minute to check the motor was still running after transport. I bought it because it had been well looked after and at a price that suited me, I`m in no rush to use it - but at the same extent - you can sit looking at it all day but if I don`t ask the questions I`ll never learn - the next step would then be turning it on.

I have no option but to wait for another few weeks before I try it as I need a collet set before I dare hold a cutter. I`m not trying to rush - things have moved fast - I now have three machines, but I`m learning, taking my time and doing my best. I need to start with the basics and that is why I am asking basic questions. Reading back over my post - I suppose I`m not necessarly asking "how would I make that part", I`m wanting to know the basics about how that part is made....just trying to learn! It is difficult with only books and the internet...

I mean simplify the first one - lets just say I wanted to turn a 0.5" ally block 8"x4" into a 0.5" ally block 2"x2".
Would I cut the excess by hand or cut it directly out of the block on the mill? Presuming I can set the block up square - would I mill the edges true with the side of the end-mill with the piece on an overhang or would I hold the piece vertically on vice and use the end of the endmill?

It is these sort of basics I want to know .... I`m no-where near the mill yet.

[Darren]

Cut it down nearer to size with some sort of saw first, milling is slow 

[raynerd]

Hey Darren, you won`t believe me but that has helped a lot - I guessed that that was the score but wasn`t 100%. Would you then stand the piece vertically and mill the top with an end-mill or would you overhang the piece horizontally over the edge off the vice and run the endmill down the side?

BTW - just looked at your T-nuts thread again - excellent, certainly a neat little project I may try first when it comes to it.

Chris

[Darren]

It all depends on the size of the part, you want to look for max rigidity. Any vibration will cause problems.
If it vibrates enough major problems like a snapped milling cutter flying at frightening speeds across the workshop, maybe towards you !!

Don't ask me how I know ....

[matnewsholme]

Chris

a decent start would be to get a copy of 'milling- a complete course) by harold hall from the wokshop practice series of books. It got me going with your mill and it starts from basics and gradually builds up in complexity. only about six quid or website is currently doing a buy 2 get one free offer so you could get the lathe-complete course and new mini lathe books at same time for about 12 quid. lots of info in there to get you going

Matt

[kvom]

Would you then stand the piece vertically and mill the top with an end-mill or would you overhang the piece horizontally over the edge off the vice and run the endmill down the side?

You can do either.  I get a better finish from the end flutes than the side flutes, so that is my preference.  However, if the piece is too long or too thin then the side should/must be used. 

Your bracket doesn't look as if it needs a high level of precision, so I think you should be able to make it work once you know how to operate the mill safely, as John says.

One approach on the slots is to drill a series of holes, then join them with an endmill.

The central hole is likely larger than any drill you'll have, so it will have to be made with either a boring bar or a rotary table.

For the corner angles you will need something (e.g., angle bar or protractor) to set the piece in the vise correctly.

[raynerd]

Cheers, Matt. I will do that - infact I may nip to rdgtools after work or Sat and pick up a copy.

Kvom - when you say a boring bar, on the lathe in a 4 jaw?

Chris

EDIT: I presume it would be easier on the mill :http://www.jjjtrain.com/vms/mill_boring/mill_boring_00.html

PS Thanks john for the links - very very good!

[bogstandard]

Chris,

Holding the job safely is the most important thing in milling.

If you have a block that is rough sawn with nothing square on all six sides, how do you hold it in a perfectly parallel set of jaws without it becoming loose and flying out of the jaws? And no, belting on the vice handle with a big hammer isn't the answer. I will give you the answer with one of my c-o-c's.

You mount the part with the straightest edge against the fixed jaw, and the piece of ali bar trapped between the piece part and the moveable jaw. By very carefully skimming the top face down, you will end up with a perfectly flat face. That flat face is then put against the fixed jaw and again with the bit of ali in the same position. The second face is then gently cut.

The first face is then set down onto a parallel with the now flat second face against the fixed jaw, again the piece of ali is put in.
The third face is now cut.

You will now have three faces square to each adjoining face, and sides 1 & 3 will be parallel to each other. By setting the second side down onto parallels, and sides 1 & 3 clamped between the jaws, the ali bit is now finished with, and by cutting across the top face, all sides should be parallel and square to each other.

There are a few ways to get the ends straight and square, but I will let you find that out for yourself.

I will keep saying this, there are no shortcuts, this was just getting a bit of metal squared up, and that is only one job from millions upon millions that you could come across. You need to get the basic techniques under your belt before even considering jobs that require maybe a couple of dozen, or sometimes hundreds of operations to make one part.

If you notice Darren, he has done almost everything off his own back, the hard way, basically by trial and error, and he will tell you, it is a very expensive way to go. But I am sure he now realises, that if he had sorted the basics out to begin with, his journey would have been a lot smoother and less costly.

I know it is difficult for you, but just to reiterate, for someone to write down everything that you would ask for would be a full time job. I taught John S over the internet by emails how to machine his way to success, day after day for well over two years, he is making lovely stuff all by himself now, with just the occasional question from him and answer from me. I have my own mentor, and occassionally I seek his advice over how to machine something up, and I am sure, if his mentor was still alive, he would put questions to him.

Very few jobs are as straightforwards as you think, and not all can be learned in a few weeks.

Getting back to your original post of how would I make that.

Over on HMEM, and the article should still be over there somewhere, a gent asked if I could help him out to cut a fairly easy cam using the RT. I stayed awake almost all night writing it up, move to this angle, offset in the X to this setting etc. and posting it onto the site. By following my instructions to the letter, he had the job done in next to no time. Would I do it again, a definite no. But I will help someone as much as I can, if they are willing to put the same amount of work or even more to help gain the knowledge and experience.

This post has most probably taken me more than an hour. So Chris, what hours knowledge are you going to learn on your own in return?

John (after his pound of flesh)

[CrewCab]

when you say a boring bar, on the lathe in a 4 jaw?

Another way, and perhaps more suited would be to securely clamp the work to a faceplate, you might need to pack it off a little as well to avoid cutting the faceplate with the boring bar.

The guys are right in that work holding is one of the most important aspects of milling, it quite often takes much longer to set up a job than actually do the machining.  Your quite right to ask, just take it a step at a time, and most of all stay safe.

CC

[Stilldrillin]

Very well explained John..... 

By `ek you`ve got much more time & patience than me! 

David D

[Darren]

If you notice Darren, he has done almost everything off his own back, the hard way, basically by trial and error, and he will tell you, it is a very expensive way to go. But I am sure he now realises, that if he had sorted the basics out to begin with, his journey would have been a lot smoother and less costly.

I'm not quite sure that's how I see it?

I enjoyed myself, I learn't a lot and it didn't cost that much?, about the same as buying the tools I made, roughly....

Plus I know now how to deal with some really difficult materials that many wouldn't attempt to use in the first place.


My two penith....

[SPiN Racing]

My 2CP on the whole thing....


Listen to John... Listen to the guys here.


I am very new to things. VERY NEW. The biggest thing you can do is read the writeups. How are other guys going about making things?  What are they doing.. and try to figure out how what you want to do overlaps with thier stuff.

The Project builds are a great teaching tool. Read them. The guys have a ton of info in there.. and it may seem it doesnt always apply to what you want to do.. but you will be reading them and suddenly the light goes on.. and you think.. OH WAIT... THAAAAATTTTTSSSS how you do that!!!


I would think.. Make sure you have stuff locked down. Learn to tram the head of the Mill. And then CAREFULLY SLOWLY start making shavings.  Try with making a block smaller. Pick a size in your head. And go for it.  If its 5x7x3  Make it 4.5x6.5x2.5  And see how accurate you can get it.

If you do fine.. YAY! Pick something else to try.
If you dont.. try to make it a little smaller accurately.

Pick something "simple" to make. Something you want to make. SO you are motivated to make it.. and then carefully start trying to make it.

Read everything you can about making that item.. search all over. Watch clips, and read writeups.
The knowledge of how to make them and the techniques are not things you know automatically so a bit of searching and reading for the tricks is the way to go.  I found I thought "hey.. here is how I would do this..." then I looked around afterwards and people were doing the same thing like 100 times easier and faster. I just hadnt seen it before. /shrug

Good Swarf Making!! 

[CrewCab]

When I decided to have a go at single point threading I bought a few bits of Delrin (or Acetal), it's an engineering plastic, pretty cheap and easy to machine ........... so good to practice with.

CC

[zeusrekning]

All right let me put my poot in. How would I make this part in my home shop? That can be answered so many different ways. Multiply that by the number of different ways other people would make it. Then again figure in all the different ways dependent on what tooling is available. See where this is going. What im getting at is this is how I would make this part in MY shop.

First my assumptions.
1. The center bore diameter is critical.
2. The location between the center bore and the bolt circle and slots are critical.
3. That the outside profile is not so critical.
4. Material is to correct thickness.
5. Material is not correct width and saw cut to length.
6. The part is symmetrical with the bore being centered (two slots , one on each end).
7. Looks like large bore my have a counter bore on the opposite side.
8. I assume the part is 1/2" thick, 5" wide 8" long.
9. All dimensions have been taken and a sketch made.

So how I would go about it.

I think 1/2" thick by 5" wide is too tall to stand up and machine the edges.

1st op. I would arrange my vise jaws so that I can hold on the 5" long sides (by putting the jaw on the front of the mobile jaw).
I would hang the part out of the side of the vise about 3/8" and machine the 8" long side using a common 1/2" dia HSS endmill.
I would then take the part out of the vise and deburr.
Then put the machined edge against the fixed jaw and machine the two 5" sides bringing the 8" length dimension in.
Again remove and deburr.
Now you should have a plate with 2 parallel ends and one long edge square to the two ends.
I would then hold the part long ways again and machine the 4th edge to dimension.

Now you have a plate to the correct outside dimensions all square. 
Obviously this would be easier if you had material to size but again, MY SHOP. I never have aluminum to the correct size.

Next, With my jaws in the usual position in the vise I would use parallels to space the part up so that I can grip on at least 3/8" and leave a bit of material sticking above jaws.
If there is enough material to make a fly cut I would if not I wouldn't.

I would then find the center of the plate using an edge finder and zero the good ol' DRO.
Then spot drill slightly all major features (all hole centers and the center of the slot start and end points.

I would then drill all holes to size, drill 4 holes for the slots. Depending on the size of the slots I would either use a drill the same diameter as the width of the slot or the next available size down if it is an oddball dimension for the slot width. Lets call these my slot holes.
 
Next I would use a 3/8" endmill and cut from the center of one slot hole two the other. Id prob do these in two cuts of 1/4" each. Making sure to lock the table down in X. Repeat for the other slot. Then with a good sharp 3/8" HSS endmill I would move to the center of one slot hole. Move over .04" or so and make a cut to the center of the other slot hole at full depth. (Making sure to conventional mill not climb cut) If you are not familiar figure out the difference between these two terms.
At the end of that cut I would move over the center of that slot hole +.04" and cut the other side. Then measure. After that ...... Measure again.
Your slot should be .045" narrow if all cut good. Do the math and repeat using number needed. Side point. Many DRO's have the feature when you can store datum points. It would be nice to store all feature points that you center drilled earlier. This is nice b/c then when doing the 1st slot you just move to zero of slot hole one, it will read (X0-Y0) and move over equidistant amounts.
Then do the same for the second slot.

I would then drill as big of a hole as I could for the center bore. For me this would be a hole saw prob in the 2-3/4" to 3" diameter range. I would then put the boring head in. I would make a skim cut and measure, cut and measure and so on till the bore is where it needs to be. If there is a larger counter bore I would probably machine it the same way as the bore was done. But I would use a boring bar with the leading edge as square as possible. If you use a regular bar with plenty of leading edge relief you will end up with many small steps in the bottom of the counter bore. This is the reason for wanting a square edge. I would also set my quill stop assuming that the counter bore depth is not super critical.
I would then flip the part over (after deburring) and find center of the large bore. I would then move to all four holes of the bolt circle and counter bore using the closest size endmill I have available, again using the quill stop for depth.
 
For the angles on the outside If not needed I would omit them, If needed I would first lay them out with my combination square and scribe.
Before we proceed , this may not be considered the best way but It works for me. And I'm assuming it would fit and work but may not once at the machine.

I have a set of tall jaws, I would put these in the vise. Then I would hold the part so that the corner I plan to remove is sticking above the vise. Using a parallel laying flat on top of the vise jaw I would get the scribed line parallel to the top of the vise jaw and tighten the vise. Then using an endmill I would machine down to the line. Then repeat for the other three corners.


And for the fine print.

Im sure I left something out, if not it is a good day. And If all went as planned and I didnt leave anything out Id go buy a loto ticket.

Tim

Ok I went back and reread your question. Not sure if You wanted all that I posted above or not. But for the slots it is almost always better to use a smaller endmill than what the width of the slot is finished to. The enmill will want to pull left and right and will cut poorly and prob oversized. Same for keyways,

[kvom]

Tim's advice is all good.  (I think he may have switched the edge milling on the sides, as not many home shop vises will open 8", but that's a nit). 

In looking at the motor and bracket, I would opine that your tolerances are pretty wide.  You need to get the 4 bolt holes close, but since the bolts have washers you will have no issues if they are a bit larger than the bolts.  The center hole needs to clear the motor face and leave the ventilation slots open, and the bracket slots need to match where they will be mounted.  Once again you almost certainly have a pretty wide tolerance.  The bracket thickness likely just needs to be enough so that the nose of the motor doesn't protrude.

What I am saying is that for anything you make you can decide how accurate and precise it needs to be.  Spending hours making that slot accurate to .001" will be time wasted it .1" suffices.  What people are saying here is that you should know HOW to get the .001 precision when you need it.

Having a boring head for your mill is a useful thing when you need a hole larger than your drills, esp. if it needs to be a precise size.  For this bracket, it would be much faster to set it up and cut than doing it on the lathe with the 4-jaw.  You can also enlarge a hole with the part on a rotary table using an endmill, but once again the setup is more time consuming.