MadModder
Gallery, Projects and General => How do I?? => Topic started by: John Hill on March 01, 2009, 12:25:50 AM
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I want to make myself a gimballed gyroscope. The plan is to cut the gyro wheel and the gimbal rings from a sheet of 1/4" plate.
The first experiment was a bit of a failure, I put a square of plate in the 4 jaw chuck and made a trepanning tool. The first cut was to cut the gyro wheel itself and it came out clean enough. Cutting the first ring started OK then the tool began to chatter and no amount of phutzing with the tool tip seemed to make a difference, the only thing that would stop the chatter was to increase the feed pressure.
You can imagine what happened, when the tool broke through the ring tumbled out, got tangled and ended up twisted like a pretzel though it didnt stall the lathe or seem to do any damage except to the tool tip. Oh well...
So, what is the orthodox way of cutting a ring from a sheet?
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Hi John
What diameter disc are you after making ?.
Bernd started a thread on some trepanning he did that may help
http://madmodder.net/index.php?topic=624.0
If the problem is the disc flicking out when the tool breaks through you could try sticking it to the back plate with some two way tape or supper glue (tape would be best) before you start.
Hope this helps
Stew
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Stew, the first cut, the solid disc, is 50mm diameter, the ring about 70mm.
Yes, the ring being cut off has to be restrained somehow, I will need to get some more steel so that I can have a sacrificial backing on the plate as using the 4 jaw chuck is obviously not going to work unless I can think of a way or restraining the cut off bits.
I dont think I need a tool like Bernd made unless I go up in size a little!
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John
John or was it Ralph ?. :scratch:
Had a link friction turning some hubs for a fly wheel that will do what you want.
Basically what you do it rough your disc out with a saw, put a centre in the middle on a pillar drill, put some masking tape on the back of the disc then trap the disc up against the chuck jaws with a running centre and trim up the OD.
If you do a search of the forum you may find the link or perhaps John/Ralph will point you to it when they read this.
Just read your post again 50mm and 70mm (2" and 3") Have you thought of a tank cutter ?. When you've got the bore done you can mount it on a mandrel to trim up the OD
Good Luck
:wave:
Stew
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Hi John, the latter part of this video shows one way to go about it.
http://techtv.mit.edu/videos/172-machine-shop-10
PS, the whole series is worth a good look.. :thumbup:
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John,
If you can grind up the shaped tool, it will do the trepanning you require, it is a combination of a parting and a boring tool. Make it about 4 to 5 mm across the tip. It will scream and chatter on the way thru, but you have to be positive with it and wack it thru.
It needs to be set exactly on centre height or at most, a couple of thou high, to allow for downwards deflection.
Remember that you are coming out from the centre, so the further out you go, the speed needs to be reduced. For your first cut at 50mm it would be like cutting a 50mm bar, so get your speed down below say 400, then reduce the speed the further out you go.
I fairly regularly cut recesses in flywheels with this shaped tool, so trepanning with it should be no problem.
John
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After watchig you all working magic.. I think If I were to try to cut rings.....
Its late Im struggling for the term. Face plate chuck. With the holes.
Bolt a disk of plywood to it, say 1/4" or 3/8"
Then superglue and center Bolt the metal to it.
Then when cutting the ring.. the metal stays attached to the board after it is cut... I think. :scratch:
Im sure the more experieced members would say yes or no to that one. (listens to find out if its a decent idea)
Scott
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Ok..... So I've read this a couple of times now and from what I can figure this is the way I would tackle the issue....
Fitstly hold your square (assumed) plate to a faceplate (with sacrificial bit attached) and bore out the centre to size required,(I seem to think you don't have a mill? I did this earlier in the thread I've linked to below... Copied from Bernd :wave:)
Then using the chuck jaws through the hole you just bored, clamp the work from the inside using two paralells on opposite sides to space the work off the back of the jaws for the tool to miss the jaws :thumbup: yet keeping the work concentric.
Then just turn your outer diameter.... You should have a ring left?!
Something like this.... Go down the page 1/3rd
http://madmodder.net/index.php?topic=389.90
Hope this would work? in 1/4" plate I would think it would?
Good luck :dremel:
Ralph.
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Similar to what I did here, scroll down a bit http://madmodder.net/index.php?topic=702.0
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John H,
Here's what I would do for work holding. I would use a face plate with a sacrificial plate bolted to the faceplate, aluminum, MDF (medium density fiberboard). Take a skim cut to make sure it's square, Mount the 1/4" thick plate using four clamp plates as shown in the C-o-C below. Also grind up the tool Bog's (John) suggests and have a go at it. And like John said slow rpms. I would start at the slowest and work my way up until the tool starts to squeal. Hope this has helped.
Bernd
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OK, thanks to all. John Bogs, I made a cutting tool just like that but I had a lot of trouble with chatter even on the slowest speed though increasing the feed pressure did get the chatter (almost) under control.
No, I dont have a mill though I may have a shaper if I 'win' the auction tonight.
I will be reading through the other ideas again before making another attempt! Thanks to all.
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John
I'm making some hubs on my elbow thread that a similar in size to what your after, this may help.
Cheers
Stew
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OK, I got some progress, I got a ring cut after bolting the plate to a face plate, using a bit of board between. The board was probably a mistake as it was not true and I was too stupid to true it up! It was bolted at the corners and in the centre.
The trepanning went well when I got the tool the right shape and the right feed and speed, metal came off in long blue streamers, very pretty.
Now I have been making the hub for my gyro wheel, two pieces with a thread between. It seems that nothing is ever true once taken out of the 3 jaw and put back in! Is that normal? Even when I centre drill the work before taking out and use the tail stock to centre it when putting it back it is ever only close.
Yes, I know :worthless: but the camera is not here right now. :beer:
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John
It depends what you mean by true ?, a good chuck will only repeat to a couple of 0.001" you'll find that it will perform better using one position to tighten up on experiment to find the best.
If you want better that this you'll have to change your holding technique, collets, or even working of a bespocke mandrell turned up and kept in the chuck so that you can load and unload the work from it, or work from a four jaw and clock the work up each time you load it.
One problem you may be finding with the discs is that its not going in flat you may have to put a stop behind it in the chuck to push up against to ensure its flat.
Hope this helps
Stew
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John,
Stew has hit the nail on the head.
Accuracy always comes at a price. That is a fact of life. Either you have to spend time setting up with a four jaw independant, waste materials to make holding mandrels, that can only be used the once, because when they are taken out of the chuck, they will have to be recut, as they lose all concentricity as soon as you slacken off the chuck jaws. Or you purchase items that will allow you to get the repeatable accuracy that you require.
I am the type who will spend cash to get it, I am not boasting or gloating about it, It is just that I class my time as more precious than cash, and I need it to carry out the jobs I do for monetary exchange. But don't get me wrong, I am not silly about it, if I can get something cheaper to do the job, I will do, I don't go for the most expensive bits, like some people do. But at times, quality does make a huge difference. The cost of machine tooling for say a new lathe, will cost between about 50% to over 100% of the cost of the original machine. Again hard facts of life.
Not everyone has that facility, again, a fact of life, and doing it on a shoestring is nothing to be ashamed of, family and personal needs must always come first. So in that situation, you usually have to do it the long and hard way.
I have found and always said, that the cheapest way to get spot on accuracy for circular parts using a 3 jaw is to invest in a set of soft jaws for your chuck. Mine cost me about 20 to 30 squid a set, and I have them for every self centring chuck I own. If they are used intelligently, they will easily last the life of a chuck (again, I will replace my most used chucks every few years, they do wear over time).
If I get the time over the next few weeks, I will do a bit of a write up to show you how to easily improve your accuracy, either with standard practices, or spending a little cash, to make it a permanent thing.
John
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Thanks Stew, John
Now why didnt I know that the accuracy question could be solved with money? :D
Actually, I thought I had the solution when I made a mandrel for the MT3 but thats not very repeatable either and I dont know why, maybe my taper is not at good as I thought it was. :(
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Actually, I thought I had the solution when I made a mandrel for the MT3 but thats not very repeatable either and I dont know why, maybe my taper is not at good as I thought it was. :(
John, if your MT3 mandrel is not repeating, depending upon how you made it, it is probably dirt or chips inside the bore or on the taper. The mandrel SHOULD be made from oversized stock. Drill and tap for the drawbar first. Then cut the taper. Now, clean the bore, really clean, make sure there are no imbedded chips or dirt or oil in it. Put the new taper in the bore and fasten it in with the drawbar.
Do the rest of the turning to size and facing operations with it held that way. So long as your spindle is not worn out and is rotating true, you should end up with a very repeatable arbor.
Alan
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Thanks Alan.
I think I found the reason why my mandrel is not as good as I would have liked and that is that the face I press the work up too is not of a big enough diameter and has too little area to locate the work, I think that face should have been turned a little concave too? I usually pay good attention to the chips and dirt issue and have a 'special' rag that is used only for wiping our tapers and the bits that go in them.
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Thanks Alan.
I think I found the reason why my mandrel is not as good as I would have liked and that is that the face I press the work up too is not of a big enough diameter and has too little area to locate the work, I think that face should have been turned a little concave too? I usually pay good attention to the chips and dirt issue and have a 'special' rag that is used only for wiping our tapers and the bits that go in them.
John,
There may be a small radius where the face meets the mandrel. A little undercutting just at that point may make a world of difference. The face shouldn't really need to be concave, just make absolutely sure it's not convex instead.
Alan
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Yes Alan, a little undercutting does describe it better. Hopefully, armed with what I have learned on this thread I will have more success next time I need to use a mandrel.