Building a milling machine

[NormanV]

I have been busy today. I gave quite a bit of thought to Pekka's comments and decided that I would be able to do it the "normal" way after all. The milling spindle has a 12mm thread (not 10mm as I originally thought) to which I can attached the splined shaft, that should be plenty strong enough to transmit enough torque for even a large fly cutter.
I have made the patterns for the mounting brackets for the pulley and I think that they will do the job. The attached photo shows the patterns mounted in place to show how it would fit together.
Unfortunately the weather forecast for the next couple of days is not too good so I will have to be patient.
I do not plan to make the splined shaft myself and was thinking of trying to find a shaft from a gearbox that might suit as my original search found one that was priced at over £50. I searched some more today and found a supplier who can provide what I need for only £20. I shall get it ordered tomorrow.
Norman

[NormanV]

I've just had a bit of a disappointing pour. All seemed to be going well but nothing came up the riser. I assumed that the mould had collapsed and went back inside to watch the Canadian Gran Prix practice session on TV. Things got worse, Lewis Hamilton is not the top of the board!
When it had cooled down I opened up the mould ant to my surprise I had a complete casting, it appeared that when I poked a rod into the sand to rap the pattern I had loosened some sand right on the exit corner and blocked it enough to stop the metal but it allowed the air to escape.
There was a bit of a collapse but I think that I can clear that with a grinder. I had to have two goes at making the mould, I don't want to have to do the whole thing again. Once I've cut it back with the grinder it will do fine, plus it won't show!

[NormanV]

Here are the four castings that I need to mount the pulley above the head of the machine. The two square pieces are for the bearings. The two main castings are too big for me to machine so I made the bearing mounts separate so that I can easily machine them and then align them accurately before fixing them in position.

[PekkaNF]

I really wish I had courage to try casting and had even 1/4 of your skills. To me those look incredibly good. Casting really saves effort on turning/milling from solid and gives much freedom on design.

Pekka

[awemawson]

  Looking very good Norman - you must be pleased 

I take it you've been back to the scrappy and got some more aluminium?

[NormanV]

Pekka, you should give it a try, it is not really all that difficult. Once you've done your first one you will wonder what all the fuss is about. The most important part is getting the patterns right, I am not very patient and my patterns are not particularly neat or accurate but they are just about good enough.
Not yet Andrew, but my stocks are getting low!

[NormanV]

The bearings for the drive pulley arrived this morning and it was a pleasure to do some work on the lathe for a change. I have machined the castings to mount the bearings and this afternoon I will get the castings mounted on the bracket that I made last week. I'm still waiting for the splined shaft to arrive so that I can get the backet fixed to the top of the machine.

[NormanV]

I'm cheesed off with suppliers, the bearings that I mounted today were ordered yesterday and arrived by post today, postage cost £1.50. Great! Thank you www.simplybearings.co.uk
On Friday morning I ordered and paid for the splined shaft I had to pay £9.50 for next day delivery (that is all they offered, they would not post them), today is Tuesday and they still haven't arrived. When I tried to chase them up the supplier wasn't interested. Aargh!!!

[NormanV]

I made a great leap forward today! The splined shaft had caused me problems, it needed to have one end turned down and threaded 12mm. I have an imperial lathe so I tried to thread it with a die, of course it turned out crooked! I admitted defeat and went to a local engineering firm who quoted me £15 to thread it for me. It sounded a bargain so I left it with them. I collected it today and rushed home to fit it, perfection!!!!!
I have now mounted the castings that support the top pulley and everything is turning freely.
The next job is to machine the pulleys, I have decided to use poly V belt as the thinness gives me more clearance around the top casting.
After much searching I managed to find the dimensions for the pulley grooves, now I have to grind a tool to cut them. Does anybody have suggestions on how I can grind it accurately enough to fit the belt?

[NormanV]

You may notice the "flywheel" looking object above the head casting. That is a bit of the design of which I am rather pleased. The main spindle is a 25mm spindle with an E32 collet chuck built in. It is mounted in taper roller bearings and needs some way to preload the bearings.
I bought a taperlock bush and pulley. I drilled and tapped the bush to take 4 grub screws that bear on the rim of the top bearing, this enables me to adjust the preload precisely. I turned the flanges off the pulley as they were getting in the way.

[Manxmodder]

Hi Norman, it is certainly looking very much like a functional milling machine now.

I agree with your sensible choice to use poly V belts for the drive and I wonder if there are any of the propriety brands of carbide inserts that are the correct angle for machining the multiple Vees.

What are the angles and dimensions in the info you have obtained?......OZ.

[NormanV]

Hi Oz, attached is the details that I have found. The groove is 40 degree angle, which unfortunately does not fit any thread gauge.

[philf]

Hi Norman, it is certainly looking very much like a functional milling machine now.

I agree with your sensible choice to use poly V belts for the drive and I wonder if there are any of the propriety brands of carbide inserts that are the correct angle for machining the multiple Vees.

What are the angles and dimensions in the info you have obtained?......OZ.

OZ,

There was some discussion on Poly V pulleys some time ago. http://madmodder.net/index.php/topic,8306.msg89232.html#msg89232

Carbide inserts are available but for one groove at a time - http://www.premierformtools.co.uk/pdf/EZG24.pdf - I've no idea how much they cost or if they are available in one-offs.

I've ground a tool up for J section belts which I've used to machine many Poly V pulleys. It can't generate the radius on the crest of the grooves but that never seems to have caused me any problems.

Cheers.

Phil.

[NormanV]

Phil, how did you get the angle correct?

[Manxmodder]

Cheers for the links Phil,

The earlier Madmodder article is really good but would have been really interesting to see how the OP's homemade pulleys turned out.

I note that John Stevenson reckons 55 degree tools are ok and the belts will adapt themselves and bed in with use.

If that is the case then a 55 deg. threading insert or a 55deg DCMT rhombic style insert would be suitable....OZ.

Edit to add link to DCGT 55 degree rhombic inserts best for aluminium turning and available with 0.2- 0.8 mm nose radius.
http://www.shop-apt.co.uk/carbide-inserts-for-turning-aluminium-alloys-non-ferrous-metals-plastics/dcgt-11t304-alu-ak10-carbide-inserts-for-turning-ground-and-polished-for-aluminium-uni-tip.html

[philf]

Phil, how did you get the angle correct?

Hi,

I had access to a huge profile projector where I could project a magnified image of the tool onto a screen to which I clipped a 20:1 or 50:1 (can't remember exactly) template drawn on to translucent drawing film. I ground and stoned the 40 degree profile and root radius to the template.

Now I'd use my Quorn T&C grinder to do the 40 degree form but would probably still stone a radius on the end.

For hobby use I don't think the angles and radii are super-critical but I would imagine that 55 degree grooves are a bit too far out and would lead to vastly accelerated wear and slippage.

Phil.

[NormanV]

I saw JS's comment that 55degrees would do. That happens to be the size of the only carbide tip that I have. I could use it but I have quite a lot of work invested in one of my pulleys and have no desire to mess it up. So, what depth should I cut each groove?
Phil, I fear that you are correct concerning the wear.
45 years ago I worked as a draughtsman at an engineering company and one task I had was to produce drawings at 10 times size to an accuracy of 100th inch to place on a "Shadowgraph" machine to check the profile of parts to 1000th inch. I had good eyesight in those days!

[vtsteam]

If you have access to an ordinary computer scanner, put the tool you are grinding on it and scan it. You can then just blow it up in any paint program to measure angles and check profiles. 

Distortion is minimal compared to a camera, and even a cheap scanner these days will scan at 2400 DPI or better, which can be blown up tremendously. Photos on this forum are probably displaying on your monitor at 96 DPI, to give you some idea of the degree of enlargement possible.

[NormanV]

Good idea Steve, I hadn't thought of that. It's a bit slower than the shadowgraph machine but will do the job.
Thanks.

[vtsteam]

Norman, I've often used my scanner as a microscope for small objects. I once wanted to identify seeds that mice were storing -- it's amazing the detail you can get.

Also if you lay a rule alongside the object, you can scale from it.

You can also work out a calibration from a scanned standard for future use. Screw threads can be looked at, etc. Gets a little more use out of an old scanner than it usually gets otherwise.

[NormanV]

I did lay a ruler alongside it on the first scan but didn't bother on further scans as it was just the angle that I was interested in. It took a few goes but I got there.
Machining the pulley was straightforward enough, I just had to keep a close check on the tools increments.
It turned out well.

[philf]

That didn't take long Norman!

[vtsteam]

Looks good! 

[NormanV]

I machined the motor pulley this morning. It did not go as well as the first pulley. You can see from the photo that the sides of the grooves broke up on the smaller part of the pulley. I'm not sure why that was, it wasn't caused by a blunt tool as I cut that section first and you can see that I didn't have the same problem on the larger diameter. It may be a casting fault.
Since machining it I have cleaned it up with a file and emery, it looks better.
This afternoon I was planning to cast the motor mounting plate, I'll cast a new motor pulley at the same time.

[NormanV]

I got lazy and decided not to do any casting today. Instead of making a  mounting plate for the motor to allow it to pivot when adjusting the belt tension I decided to mount the motor on four studs. It will take longer to adjust but it's not a job I expect to have to do too often.
Everything is now ready for the belt, that should be here on Tuesday.
Now I have to do the wiring for the drive motor with it's speed controller, the reversing switch on the motor for  raising and lowering the table and the tachometer.  It's mounting the switches that is giving me problems. Where should I put them? I suppose I could cast a nice box to fix to the side of the head. I am not keen on putting the switches on the mounting bench due to the danger of swarf getting in.