Author Topic: Another homemade milling machine  (Read 7261 times)

Offline AdeV

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Re: Another homemade milling machine
« Reply #50 on: April 18, 2017, 12:05:28 AM »
Since it's only the weight you're after, and not the constructional qualities, why not just use a bag of sand? Seal the bottom as best you can, but leave a removable panel; pour sand in the top until desired weight is achieved - it'll find its own way past the internal structures obviously. Then, when you need to move the machine at a later date you can simply open the removable panel and let the sand out...

The only thing you need to be sure of is that the sand is bone dry before you pour it in, wet sand will cause untold rustiness...
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Online awemawson

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Re: Another homemade milling machine
« Reply #51 on: April 18, 2017, 02:18:34 AM »
If it's a closed box structure i.e. No holes for stuff to flow out, dry sand or pea shingle will work just as effectively as concrete, and will settle into a dense packing over time. Also in extremiss it can be removed if you make a suitable plugged hole in the base.
Andrew Mawson
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Offline PekkaNF

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Re: Another homemade milling machine
« Reply #52 on: April 18, 2017, 03:26:57 AM »


I like the idea of filling with concrete. Adding mass is one of the simplest things you can do to a small machine to improve it.......

PK
I do too but Pekka disagrees and I see his point about shrinkage. However upon doing some extra reading it seems that most of the shrinkage comes from adding more water than is needed to make the concrete move better it seems that if the added water is calculated correctly then little shrinkage occurs but the mix is extremely thick. Will have to look into it a bit more.

The thing is that concrete shrinks for 400 years. First faster and then slower. Many factors affect on shrink rate and some you have influence and some not.

Worst shape for concrete "filled machine" is a hollow thin steel section that you fill with concrete...some machine manufacturers tried this -70/80:s and failed. Concrete filling will shrink in time and delaminate from the skin...if you weld rebar to avoid that it will pull the skin out of alingnment. There are ways to reduce the shrink rate or compensate it, but it will not work in machine building scale.

You can make a servisable machine if you know what you are doing. Basically you cast more or less square section, no voids in it, you may cast some features to it. You don't need rebar and other "iron" on it, unless you have hanging beam or such bad idea. And then let it cure and age some time - longer the better. Then use this cast as a sandwitch between steel members and have it on compression. You must use epoxy concrete, injection epoxy or grind the concrete surface flat prior mechanically mounting the steel sructure to it.

Epoxy concrete works.

And as Andrew et.al. said sand or such will dampen "ringing" pretty well too, it's cheap, reversible and has all good qualities to home build.

Pekka

Offline shipto

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Re: Another homemade milling machine
« Reply #53 on: April 18, 2017, 05:13:57 AM »
What about a dry mix? www.precast.org

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Online awemawson

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Re: Another homemade milling machine
« Reply #54 on: April 18, 2017, 05:38:13 AM »
It will eventually harden from moisture in the air and you'll lose the advantage of being able to remove it.
Andrew Mawson
East Sussex

Offline shipto

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Re: Another homemade milling machine
« Reply #55 on: April 18, 2017, 06:07:15 AM »
Won't want to removed it there's nothing I need to do from inside. The only advantage of being able to remove it would be weight but once it's in place it would be my kids job to get rid of it 😃

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Offline mattinker

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Re: Another homemade milling machine
« Reply #56 on: April 18, 2017, 06:32:14 AM »
If you want weight only, lead!

Regards, Matthew

Offline shipto

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Re: Another homemade milling machine
« Reply #57 on: April 18, 2017, 06:42:16 AM »
It's not just weight it's helping rigidity too. However as I have said I won't make a decision until it's running and I have tested to see if it's needed, fingers crossed it won't need anything extra.

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Offline PK

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Re: Another homemade milling machine
« Reply #58 on: April 18, 2017, 06:49:35 AM »
If you want weight only, lead!
In my experience....

Mass is the main advantage. Particularly on a small machine as it reduces the resonant frequency of the structure below the excitation frequency of the spindle+tooth count combination. 
This resonance (and some terrible engineering in the case of the X3 mills) is what causes the most grief, and it's why the 20KRPM Chinese spindles for chump change have revolutionised the CNC router business. They increase the excitation frequency above the resonant frequency of even the tiniest mill

But there are others.  When the structure is made up of parts of different densities, a portion of energy that travels through it as waves (rather than displacement/vibration) is reflected at each interface. This forces a portion of these waves to travel long paths and get absorbed by the substrate.

Online awemawson

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Re: Another homemade milling machine
« Reply #59 on: April 18, 2017, 07:53:09 AM »
Blimey PK that's a bit impressively technical  :bow:
Andrew Mawson
East Sussex

Offline PK

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Re: Another homemade milling machine
« Reply #60 on: April 18, 2017, 09:26:04 AM »
Blimey PK that's a bit impressively technical  :bow:
Yeah, sorry 'bout that. It was a big chunk of my PhD.... Buy me two beers and I can bore you to death with the numbers... Oh, and I've had two beers......

Offline PekkaNF

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Re: Another homemade milling machine
« Reply #61 on: April 18, 2017, 10:15:38 AM »
Blimey PK that's a bit impressively technical  :bow:
Yeah, sorry 'bout that. It was a big chunk of my PhD.... Buy me two beers and I can bore you to death with the numbers... Oh, and I've had two beers......

By all means. I'll get you drunk. Please tell more! I used go on trips with one professor, we hooked acceleration sensors and other transduces to measure vibration and find out excitation sources/sympathic frequences. Laymen had no idea how involved in real life it is.

And granules are different animals. We measured some of them too in one big machine...Big beam filled with sand or glassballs...So, which one is "better"? it all depends what is your question.

So...all this is pretty basic (from post #44):
http://www.mech.utah.edu/~bamberg/research/ConcreteCastDamper/concreteCastDamper.html

Everyone seriously considering should least read this:
https://pdfs.semanticscholar.org/5487/82f4c63376150991dd323d0ef15a7da2fee8.pdf

At this phase of this project it's all pretty academic and best to forge forward.

Pekka

Offline shipto

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Re: Another homemade milling machine
« Reply #62 on: April 18, 2017, 01:28:29 PM »

At this phase of this project it's all pretty academic and best to forge forward.

Pekka
I agree I didnt intend it to get this much of a discussion its more a "what if" situtation at the moment I could get it set up and it runs like a dream or it could be so bad that I scrap all but the expensive bits and not even want to waste a bag of cement. I hope it the first option  :lol:
« Last Edit: April 18, 2017, 03:18:21 PM by shipto »
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Offline shipto

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Re: Another homemade milling machine
« Reply #63 on: April 23, 2017, 04:28:47 PM »
So I have now turned my attention to the knee slides and in yet another operation that would have been done better with a mill I made 4 elongated slots in each and made some blocks to help me get them lined up straight and keep them there. I have decided that I will get one side lined up as best as I can to the column and pin it, then everything will be lined up to that.
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Offline shipto

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Re: Another homemade milling machine
« Reply #64 on: April 27, 2017, 05:24:39 PM »
The knee is going to have to go back to the drawing board (what theres a drawing board?) at the very least temporarily as the bits are nowhere near straight I suspect its down to the rubbish jig I made to mill them on the lathe. So I am thinking of borrowing ideas from the gingery lathe and make the ways and carriage from some bright drawn stock which will hopefully get me running the mill well enough to straighten up the cast iron bits. Finger crossed.

Nearly had a major oops moment tonight while try to move the carriage along I pushed a little too hard and dropped it amazing how fast you move when your feet are in danger  :lol: that will teach me to secure it before messing.
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Offline tom osselton

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Re: Another homemade milling machine
« Reply #65 on: April 28, 2017, 01:05:43 AM »
Yep watch them toes!

Offline shipto

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Re: Another homemade milling machine
« Reply #66 on: April 28, 2017, 07:35:11 AM »
I do wear steel toecap boots but I doubt they would have helped the rest of my foot.

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Offline vtsteam

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Re: Another homemade milling machine
« Reply #67 on: April 30, 2017, 09:52:25 AM »
Back for a visit, and a great project. I keep skipping over theory and advice posts, Dwayne, to settle on the best part of a build, the build itself! Keep on truckin' buddy, yer doin' great!  :clap: :clap: :clap: :clap:
I love it when a Plan B comes together!
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Offline shipto

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Re: Another homemade milling machine
« Reply #68 on: April 30, 2017, 05:32:26 PM »
Thanks Vtsteam
This project is going to take a little detour now in terms of the column, up until I got my Harrison I was using a past its best Drummond round bed with a broken head casting, this has been stuck under the bench slowly getting covered in various bit and pieces.
While sat in shed talking to my mate about the problems with the knee slide and how I was going to have to get something rigged up to sort them out properly it suddenly came to mind.
So I dragged it out and we sat there some more making plans and it is going to be used for the time being, this way I will have a milling machine hopefully capable of allowing me to make the origional design much better.
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Offline shipto

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Re: Another homemade milling machine
« Reply #69 on: May 01, 2017, 02:46:01 PM »
It almost feels like I should be showing this on a new thread but I guess I can get away with it.

So a bit of 76X38 channel is a good size to sit across the round bed from the Drummond, the main thing about this detour is to not damage the Drummond bed as I have other plans for it. I welded four bolts to the sides of the channel and cut some bit to clamp the channel, on the bottom clamp is a piece which will make sure the bed will not break under stress and also ensure the head will not move.

Next I bolted the head slide onto the 76X38 channel (which I didnt take a pic of) and fitted the head so as you can see I am still going to have both the head and the knee moveable.
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Offline vtsteam

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Re: Another homemade milling machine
« Reply #70 on: May 01, 2017, 07:53:37 PM »
Improvisation, and making one tool to make another is the name of our game, Dwayne! Looking forward to seeing how this will come together.  :beer:
I love it when a Plan B comes together!
Steve
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Offline shipto

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Re: Another homemade milling machine
« Reply #71 on: May 02, 2017, 05:20:27 PM »
Made the base while at work today and fitted the column to it tonight. I could do with a decent square as it seems a tad off but I cant be sure my set square is accurate, however there is one major problem with the 76x38 when its tight it is spreading around the bed at the bottom but not at the top so the head is being taken off square so I either need to use something better or weld something in to stop the bottom spreading.
In pic 3 I show the table in about the position it will be on the knee and the hole in the base is where I am planning to put the lifting screw for the Z axis, I would welcome opinions on wether I should move that forward nearer to the center of the travel? my first thoughts where that the screw should be reasonably close to the column to ensure the knee would move smoothly but I am not too sure now.
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Offline vtsteam

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Re: Another homemade milling machine
« Reply #72 on: May 02, 2017, 05:36:09 PM »
I'd vote for the center of the X and Y travels on their slide ways should be under the axis of the head spindle. And the Z screw also under that point.
I love it when a Plan B comes together!
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Offline vtsteam

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Re: Another homemade milling machine
« Reply #73 on: May 02, 2017, 05:41:36 PM »
With regard to the channel guide on the head, maybe I might try adding two small plates welded to form a Vee inside the channel legs, so the pillar now slides against that Vee. Each plate would weld to a leg, and to the channel center line, inside.
I love it when a Plan B comes together!
Steve
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Offline shipto

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Re: Another homemade milling machine
« Reply #74 on: May 03, 2017, 06:52:49 AM »
The center of the X and Y will be under the spindle axis to maximise the cutting area. Looking at most of the milling machines on a Google image search shows me manufacturers don't seem to have any rules regarding the position of the lift screw. However my machine is no where near the weights they are dealing with so under the spindle axis seems reasonable to me too. As for the head I think I am going to trap a block between the column and the channel for now and sort it out properly later. Now it is annoying me as the plan for the Drummond bed was to one day make it into a decent and saleable lathe again but I am liking the way this is going so much that it's unlikely I will change it now. So sorry to anyone who was following me while I wasted time up to now.

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