Author Topic: Building a milling machine (Read 112584 times)

awemawson · « **Reply #150 on:** July 07, 2014, 05:05:23 PM »

Try it on the lathe and report back

philf · « **Reply #151 on:** July 07, 2014, 05:16:58 PM »

Norman,

I agree with Andrew. It's a proximity sensor and not a Hall effect sensor so no magnet is necessary - just a hole. The problem with 1 hole is that you may have balance problems. If your Tacho has a divide by 2 function 2 holes would be better.

On my mill I did use a Hall Effect sensor and 1 magnet in an aluminium Poly V pulley. To balance it I glued a piece of same size stainless steel 180 degrees from the magnet. It quite happily runs at 10,000rpm.

Phil.

vtsteam · « **Reply #152 on:** July 08, 2014, 11:31:59 AM »

Drill out the magnet, tap, replace with a grub screw about half the depth of the hole in length. You should be able to balance with the screw proud, which should also trigger the sensor. When both balanced and registering on the tach, Loctite it.

Watch out for the magnet dust -- it isn't healthy stuff.

ps. but first check the sensor on lathe per Andrew.

NormanV · « **Reply #153 on:** July 20, 2014, 10:10:55 AM »

I followed Steve's advice and the tachometer is now working. I've also completed the switch panel, I added some graphics to remind me which way to turn the knobs. I'm quite pleased with it.
I've now got to save up to buy a compound table to finish it off.

awemawson · « **Reply #154 on:** July 20, 2014, 11:20:01 AM »

Glad it's now working

But from a safety point of view I'm not keen on the protruding screw. Have you tried triggering off the hole that the screw occupies? It should work.

NormanV · « **Reply #155 on:** July 20, 2014, 11:56:11 AM »

Andrew, it didn't trigger from the hole alone. I was concerned about the screw sticking out also, I will build a guard to cover the it.

Arbalist · « **Reply #156 on:** July 20, 2014, 02:02:25 PM »

Looking good Norman!

Where did you get the tachometer and proximity sensor?

vtsteam · « **Reply #157 on:** July 20, 2014, 02:18:04 PM »

What is the pulley made from -- I had thought you had cast it from aluminum, Norman. If ferrous, I can see why Andrew says it could be done with a hole. Or do these things merely need a conductor of any sort passing by?

It seems like there is a fairly large gap to the transducer -- did you try it closer with the hole?

awemawson · « **Reply #158 on:** July 20, 2014, 03:44:03 PM »

Most proximity sensors will work on a 1/4" hole in a rotating wheel or whatever. But they do vary in sensitivity. most work in the 1 to 3 mm range.

I've worked on many machines where the detector is sensing the hole for a grub screw that retains the part on a shaft

NormanV · « **Reply #159 on:** July 20, 2014, 03:47:20 PM »

Arbalist, I bought the tachometer on Ebay, item number 261307045946.
Steve, I have just been out to the workshop to check it again. The transducer does not see the hole even when it is just 1mm from the pulley. The pulley is in fact cast iron, it is a taperlock pulley that I turned the groove off as I just wanted it for locking onto the spindle of the collet chuck to allow me to fit the screws for adjusting the preload in the main bearings.

philf · « **Reply #160 on:** July 20, 2014, 04:41:31 PM »

Quote from: NormanV on July 20, 2014, 03:47:20 PM

The transducer does not see the hole even when it is just 1mm from the pulley.

Norman,

Try the sensor further away. The sensing area is usually a Gothic arch shape as wide as the sensor diameter at the face of the sensor to a point at some distance from the face. As you move the sensor further away (but still within the sensing range) you might be able to sense the hole.

The sensing distance varies greatly with material with iron being approx 3 times better than aluminium.

Phil.

awemawson · « **Reply #161 on:** July 20, 2014, 05:13:47 PM »

The eBay advert says the sensing distance is 4 mm. Quite tempting at that price to fit one to the Bridgeport, but with your experiences Norman I think I'd put a different proximity sensor on it.

NormanV · « **Reply #162 on:** July 21, 2014, 03:25:25 PM »

Joy oh joy! I tried again with the sensor reading the hole but with the sensor further away. This time I got readings throughout the speed range that agreed with the theoretical speeds of what the motor should achieve and the speed ratios of my pulleys. The readings I got are certainly accurate enough for my purposes.
Also, I have found a S/H compound table at a price that I can afford. I had previously bid on a milling machine table and slides (that would have required a lot of work) but was outbid. The compound table should only require tidying up and then I should be ready to start cutting metal!!!!!
If it all works out I have to start thinking about what I am going to make with my milling machine.
This all sounds a bit premature, let's get this machine working properly first.

awemawson · « **Reply #163 on:** July 21, 2014, 03:52:22 PM »

Hoo - blooming - ray

Norman, you'll be amused to hear I ordered one last night just to play with it - probably end up on the Bridgeport

philf · « **Reply #164 on:** July 21, 2014, 05:11:03 PM »

Quote from: NormanV on July 21, 2014, 03:25:25 PM

Joy oh joy! I tried again with the sensor reading the hole but with the sensor further away.

Norman,

I'm pleased it worked for you. It must look a lot better as well.

Phil.

NormanV · « **Reply #165 on:** July 21, 2014, 06:39:11 PM »

I don't care about it looking better, it's certainly a lot safer. It doesn't need a guard now.

Arbalist · « **Reply #166 on:** July 22, 2014, 04:50:25 AM »

Nice job Norman, it's all coming together now!

NormanV · « **Reply #167 on:** July 26, 2014, 09:55:37 AM »

I took two steps forward and four steps back today!
First I squared the head (trammed it). I followed John Doubleboost's instructions using a car brake disc. It worked but was more fiddly than I had anticipated. As I was tightening the bolts to hold it all in place I found that it altered the setting so I had to tighten the bolts alternately whilst keeping an eye on the dial gauge, but I got there in the end.
Then the big moment, I placed my newly acquired compound table onto the knee, it looked great. Then I saw the problem, a few posts back Steve commented on how far forward the spindle was in relation to the column. I had placed it there intentionally as the (new) compound table that I had intended purchasing needed it to be in that position. I have instead bought a second hand table at a third of the price of a new one but the front to back dimension is much smaller. As a consequence the spindle is too far forward. I have two options, I could fix a piece of thick sheet steel on the knee and just mount the table protruding forwards but centred under the spindle. Alternatively I could remove all of the castings above the spindle, slide back the mounting tube upon which the head and the motor are fitted and then modify the castings to suit.
It's going to be a lot of work but I think that the latter is the best way to go, at least my time costs nothing and I saved a lot on the table.
Here is a pic of it with the table in place, it really looks like a milling machine now!

Meldonmech · « **Reply #168 on:** July 26, 2014, 11:41:36 AM »

Hi Norman

The mill is looking great, you have achieved a lot, I think the decision you have made is the right one. The machine will look better and you will be happier with the result.

Good Luck with the mod Cheers David

awemawson · « **Reply #169 on:** July 26, 2014, 12:04:05 PM »

Norman,

It's looking good - you've travelled a long way making this epic casting journey

One advantage of making an adaptor plate is that larger work can over hang to the rear of the table. When I had a 'Mill Drill' years ago I did a lot of work on 19" instrument panels, and the lack of space behind the table was always a frustration on the deeper ones.

If you are not too short of 'daylight' under the spindle, you could cast a plate to adapt the table to the knee, and if in the long term you want another solution it could just be unbolted.

NormanV · « **Reply #170 on:** July 26, 2014, 12:17:39 PM »

Thank you David.
Andrew, I take your point about the extra spindle/column distance being useful but I am concerned about the rigidity or lack of it. I know that I will want more space at some time but I expect most of what I plan to do will fit within the available space with the table closer to the column.
I have examined things a little more closely and it appears that I will not have to modify any parts, just rearrange them on the tube. The only drawback will be that the motor will protrude a long way out of the back, but if I position the machine in a corner it may not be obtrusive. As a last resort I can shorten the tube.

NormanV · « **Reply #171 on:** July 26, 2014, 02:56:16 PM »

I have just stripped it down and reassembled it with the head pushed back. It almost fits. The casting marked A will have to be recast but with an overhang in the position shown by the arrow. In a way I am quite pleased as I am having withdrawal symptoms because I have not cast anything for a couple of weeks!

vtsteam · « **Reply #172 on:** July 26, 2014, 05:57:13 PM »

It's getting exciting Norman! Won't be long now before you'fre making swarf.

PekkaNF · « **Reply #173 on:** July 27, 2014, 08:07:27 AM »

It's looking very good. I'm sure you can produce some swarf with it. Try it out before painting, you find something to tinker with but after a little swarffing you know that you can do it. All machines have some limitations. Skill is that you can get the work done within those limits. If we really would make rigid enough machine, work envelope would be 100*100*150 mm, it would weight a ton and not fit into garage.

You are doing some very good work here and it has some unique features.

Pekka

NormanV · « **Reply #174 on:** July 27, 2014, 10:14:12 AM »

Thank you Pekka, I doubt that I will paint it. It will need a lot of stripping down to do that and I quite like the look of bare aluminium.
I made the new casting today. It came out better than most of my previous castings, I suppose that I must have learnt something about casting by now!
For the first time I used some aluminium swarf and bits of can in the melt and when I poured it I found loads of crud at the bottom of the crucible. The top of the melt was quite clean, it only needed minimal scraping off. It poured well but there was all this stuff at the bottom. I won't be remelting swarf in the future.

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Author Topic: Building a milling machine (Read 112584 times)