Pimping the mini-lathe

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30 Aug 2020 12:27 #180062 by RotarySMP
Replied by RotarySMP on topic Pimping the mini-lathe
It came with a datasheet, and is a PC-MINI 5 from the company Kundisch in germany. Must be pretty ancient.
The company still exists,
kundisch.de/

The guy who sold it on Ebay.kleinanzeigen.de had two of them. I am annoyed at myself for not buying both. The search I used was "industrie tastatur"
Mark

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30 Aug 2020 12:54 #180064 by RotarySMP
Replied by RotarySMP on topic Pimping the mini-lathe
I used a 1/2" ball end mill I bought from Boeing surplus years ago. I'm pretty happy with the surface finish.
Mark

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30 Aug 2020 13:20 #180067 by machinedude
Replied by machinedude on topic Pimping the mini-lathe
the big thing is to remove as much as you can with the flat end mill like you did and just leave enough to clean up with the ball endmill.. ball nose tooling is basically just a finishing tool path so .005 to.01 imperial is about all you need to leave.

the small bolts for the hold down have very little to do at this stage. the test for them is the roughing operation. so when your doing a one of it's better to go slow and easy to avoid a mishap.
the tapmatic heads are nice too but for one hole it's a bit of work setting it up. they make spring loaded tap guides that work well when you just need something quick. keeps your tap straight while to hand tap a hole. if you don't have one they can be handy for stuff like this :)

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30 Aug 2020 13:30 #180069 by RotarySMP
Replied by RotarySMP on topic Pimping the mini-lathe
I think I left 1mm for the finishing tool path, so that was probably too much. Thanks for the advice.

I have been meaning to make a tapping from from an old Emcomat dril press frame I have, but never get around to it.
Mark.

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30 Aug 2020 13:35 #180070 by machinedude
Replied by machinedude on topic Pimping the mini-lathe
drill presses work just fine with the tapmatic heads. that's where they can usually stay set up for the most part and be a time saver. they still have a place in the shop :)

i would invest in a small band saw for cutting stock, i have a cheap $200 one that i would be lost without. they are a good investment for the home shop.

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30 Aug 2020 13:50 #180073 by RotarySMP
Replied by RotarySMP on topic Pimping the mini-lathe
I have a 16" do-all, but it has tooth decay and can't use the slower metal cutting speeds till I fix it.
Mark

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06 Sep 2020 10:44 #180947 by RotarySMP
Replied by RotarySMP on topic Pimping the mini-lathe
I just uploaded Episode 29, which again has plenty of MAHO Linuxcnc converted action...

Mark
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06 Sep 2020 11:28 - 06 Sep 2020 11:33 #180963 by machinedude
Replied by machinedude on topic Pimping the mini-lathe
only clamping on the ends of the bar like you did would probably lead to some variation on the thickness from the top down to you undercut of the dovetail and the thickness across the the back side. hot rolled steel flats were probably close on the material thickness but are not flat. you could possibly get away with end clamps only if you take note of the way the bar is bowed. looking at the top down if it was a concave bow would the end clamps would pull the ends down to the table and the bow of the material would keep the center down on the table.

only problem is you force stress into the part and when the clamps are released you now have a bow in the finished part. the best way is to work the bow out of the material in a free state and once it's flat then clamp the piece down and work on the dovetails. also the grinding to part the semi finished pieces throws to much heat into your finished parts.

some times cutting a lot of material out of the center of a piece will cause the part to move from stresses in the material. so roughing the piece to so like .05 imperial over then finishing will correct this. precision machining is an art form :)
Last edit: 06 Sep 2020 11:33 by machinedude.
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06 Sep 2020 11:39 #180964 by RotarySMP
Replied by RotarySMP on topic Pimping the mini-lathe
Thanks for that explanation. I think Stefan Gotteswinter has some german play on words about work holding being harder then machining. I really should have started measuring the dovetail along the whole length and not just in the middle early as well. At least most of them will work as is, and couple will need shims, but still do the job. I've had worse failures :)

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06 Sep 2020 11:52 - 06 Sep 2020 11:53 #180966 by machinedude
Replied by machinedude on topic Pimping the mini-lathe
a good way to approach what you made would be to start with thicker material than your finished parts so you have a clamping hub. i would have cut the bar up to maybe do 2 at a time in a 6" vise and run a roughing program to remove most of the material on them first then release the part so it can move from the stresses then run them again to finish them. you don't want to hit anything down on the first operation so it can be machined in a free state. having a clamping hub gives you the ability to surface the top and all 4 side.when you flip the parts over and face the back side you do away with the need to cut them up into individual parts. and at this point you want to tap your parts down to transfer the flatness from the fist operation.
Last edit: 06 Sep 2020 11:53 by machinedude.

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