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Voicecoil
20-02-2019, 09:52 PM
After some lurking, quite a few questions, a lot of sums and some FEA I've just started building my first machine. It's not as big as I really need (I want to cut out large loudspeaker cabinets amongst other things), but I'm having a lot more difficulty finding larger premises than I thought I would. So having kind of got the bug and wanting to get on and do something I thought I'd make a small (but capable) one anyway, the experience will do me good, it will be useful for machining up metal parts and a lot of it will be transferable to the big machine design when I get the space.
Sorry I've not shared any of the initial drawings, but I don't really do 3D CAD and without being able to turn layers on and off and have the thing in your head, the 2D drawings are a bit of a nightmare to interpret. The design ethos is:
1) To try to keep all individual deflections of the gantry extrusion/side beams/bed to less than 1um for a 50N cutting force - this has been determined by calculation (thanks @routercnc for the spreadsheet) + FEA
2) Minimise twisting moments by keeping all assemblies as compact as possible - no massive spindle overhang please!
3) Keep the number of bolted joints to a minimum.
4) Try to get a good price performance compromise
It's being made out of aluminium extrusions/plate simply because I'm able to machine that better and more accurately - and you can anodise it to a nice finish :congratulatory:

Not having any CNC machining capability until it's made, I'm having to "bootstrap" the process, apart from one or two pieces that I need to get laser cut, it will all be done using the trusty Elektra Beckum chop saw, a drill press (Axminster ED16B2) and my little lathe. First job was to fettle up the saw and make a decent clamp for it:
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With a new blade fitted and a few minutes true-ing it up it goes through 15mm plate like a knife through butter. Squareness is about 0.25mm across a 125mm cut, and with a wee drop of WD40 to help the cutting, the cut ends are smooth as a b******s bottom.
First parts to make were the carriage plates for the Y axis (please note I denote X & Y from the point of view looking down at the front of the machine i.e. the X-Axis runs L to R along the gantry):
here's marking them out using the trusty optical centre punch:
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Voicecoil
27-02-2019, 08:48 PM
I've found time to do a bit more on this in the last few days, firstly got the gantry extrusion fully end drilled and tapped..... it just fitted under the pillar drill with 15mm to spare :tears_of_joy:
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talking of tapping I soon realised that there were going to be A LOT of holes to tap and if I wanted to save a lot of time (and avoid w*****s cramp!) machine tapping was the way to go. Tapping machines looked a tad expensive for the moment, thought about changing the motor of the pillar drill to give a quick reverse function, but some bits were on a couple of weeks lead time.... then I tried one of the Europa tool interrupted-thread spiral point taps:
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These seem to require a lot less tapping force than anything I've tried before and seemed hence offer up the option of tapping with a cordless drill (which convieniently has a torque limter to stop breaking taps, and a reverse to extract them). In order to keep things straight I added a circular level to the back of an old drill, using the pillar drill and a length of tool steel rod to get it properly level whilst the glue dried.
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With this and a known flat surface I seem to be able to tap holes pretty straight and all for the outlay of a 1.80 level off the Bay of fleas; and you can do it in large pieces that wouldn't fit under a normal pillar drill.

AndyUK
07-03-2019, 02:05 PM
In order to keep things straight I added a circular level to the back of an old drill

Nice bit of customisation! I've taken to using a guide for my taps to pass through; find a block of something (wood, aluminium) that is about as thick as your tap is long, minus 1cm and the length of the square drive section. Using the pillar drill, put a guide hole through the block - diameter to be as close fitting as to your tap as possible. Now you can place this block up against the surface you're going to tap, passing the tap through for the first bit of the hole - hey presto, nice and straight tapping every time.

Voicecoil
08-04-2019, 09:58 PM
I've got most of the pieces machined up now and waiting for the dozy anodisers to do their stuff on some of the beams - whilst it's obviously a home built machine I wanted it too look vaguely OK and I don't really have the space for some 3ft long anodising batths at the mo. Today I finished off making the spindle clamp, I'd cut the outside profile and done the holes a few weeks back, but I've been waiting for a friend to have some free time so I could use his mighty steam-powered lathe to bore the hole. Here it is after putting a 30mm drill through to start things off: And yes, that's a 300mm chuck and it's a heavy lump!
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Then it was something like 3 hours gentle boring out, with a few minor hiccups and several Km of swarf - here's the end result:
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The internal finish wasn't quite as good as I'd hoped as he had a rather limited range of boring bars and with 80mm of tool sticking out from the toolpost there was a certain amount of resonance going on; never mind, no-one will ever see it, and as long as it grips the spindle I'll be happy.
The reason for making the spindle clamp was initially because I couldn't easily source an 85mm part OTS, then it kind of led to some lateral thinking about how to implement the Z axis with good strength and minimum width - all will be revealed soon when I start putting it together :encouragement:

Voicecoil
20-04-2019, 02:45 PM
I've been cracking on with stuff the last few days, here's a pic of some of the parts:
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From LHS clockwise we have Z axis slide with clamp sitting on top of the bed cross beams, front bed end plates, Z axis top plate, gantry end plates and the Z axis back plate. Just hit a bit of a snag though - the big bit of plate for the top of the bed has been cut well off square by the folk at Smiths - thus even with the 2mm tolerance oversize by the time it's trued up it will be 2mm short causing a few major headaches - I will be bending their ears on Tuesday :mad:

Voicecoil
28-04-2019, 08:50 PM
Marking out the bed plate:

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I need a bigger surface plate!!!

AndyGuid
29-04-2019, 03:02 AM
Marking out the bed plate:

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I need a bigger surface plate!!!

As a pen-pusher, I'm guessing that your method is a very accurate way of manually Marking Out Using a Surface Plate and Height Gauge ?

Voicecoil
29-04-2019, 08:59 AM
Yes, I bought the height gauge and optical centre punch for this project and I've been suprised at how accurately you can do things - I reckon on smaller pieces the max error isn't much more than +/- 0.1mm and maybe twice that on longer bits: quite a novelty not to have to file out holes to get things to line up! Mind you, when you think about it people were making accurate stuff 60 to 70 years ago before CNC was even thought of, so it had to be possible.

Voicecoil
01-05-2019, 07:33 PM
Yesterday and today I've been assembling the various parts of the bed/Y-axis to check fit before doing a bit of anodising.
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All went reasonably well apart from a couple of screw heads (that need to be moved) fouling stepper motor bodies and a small CAD error on the carriage side plates that I'd transferred really precisely into metal - time to get the file out! :disillusionment:

mekanik
01-05-2019, 08:31 PM
Looking Good:thumsup::thumsup:

Voicecoil
04-05-2019, 10:37 PM
Having found it very difficult (or very expensive) to get anything done on a reasonable timescale by the local anodisers, in desperation I thought I'd have a go myself. 50 worth of chems and some plant troughs later I managed to get the gantry box done this evening, took a bit of fiddling with the process but not too shabby in the end.
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Gav74
05-05-2019, 01:56 PM
looking good

Voicecoil
09-05-2019, 05:33 PM
With all the beams now anodised I thought it was time to indulge in a bit of damping, as handling the box sections in particular showed that they were ringing a lot at mid-audio frequencies (which match up nicely with the stimulation given by typical spindle speed/cutter flutes). I thought I'd try my old fave Tecsound, but wasn't overly confident of it working as I've never used it on anything thicker than 2mm thick metal sheet before, and the box sections I've used for the side beams and gantry are 7 & 10mm thick wall. However in reality it seems to work pretty well, hanging an untreated section up on a piece of wire and giving a gentle tap with a hammer gives something not unlike a tubular bell, whereas a damped section is just a bit of a thunk. Here's some sound files from the tapping to illustrate the difference
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Looking at the decay time in an audio editor, the damping has been increased by something like 6X - a useful improvement I think - now to do some of the other parts!