I get that. When family members or friends get ripped off paying too much for house or car repairs, buying needless technology upgrades, etc., I feel the same way. But hobby stuff? That's their business. If they can afford it and they enjoy it, that's their thing. If they ask my advice before they spend the money I try to understand their goals and then give them an unbiased opinion. But if they don't ask, it's not my place to comment just to make them feel bad about their choices.
If this discussion happened before he embarked on his build and he asked for opinions, maybe the forum wisdom would have steered him towards doing a retrofit for a bunch less money. That can be great learning experience. Or maybe truly considering whether he wanted to build a machine from scratch or make parts. That conversation could have steered him to buying a used machine that's ready to cut metal for similar money. But he is where he is now, and I take him at his word that he wants to make improvements to what he's built so far. Telling him he could have spent his money or time more wisely isn't really helpful, even if it may be true from your perspective.
Maybe there's a sunk cost fallacy at play, and maybe it's foolish to keep throwing money at a project that will never be as good as something commercial. But making the most of what he has makes sense to me, since selling off his machine as-is or for parts isn't going to recoup his expenses. It's not like there's an option to turn his machine back into $30K so he can go buy a VMC. And living with it as-is may be fine, but will not scratch the "itch" he has to improve it.
I'm in a similar boat right now with much smaller budget numbers. I'm in the middle of a project trying to improve a "toy" benchtop machine that I converted 12 years ago. Does it make much sense to throw hundreds of dollars at a machine that will never be that great? No. I hope it will make the machine a little better and fix one of its major flaws, but I am aware it's a "lipstick on a pig" situation. I look at it as an excuse to learn and improve my skills that may be valuable for some future machine build. It helps that it's a hunk of cast iron I already have in the shop that mostly already works (vs acquiring something new), and that it's a small enough project that I can tackle with my available free time.
Hi ardenum,
To date my machine has cost about $30,000NZD or about $20,00USD. I'm unaware of any credible machine that I could have bought to match what I have made....unless you trot out a whole bunchdoing it yourself only makes sense if you pay less doing it than if you bought the machine off the shelf or you build something that you can't buy for a reasonable amount.
you call spending $30,000 a hobby? don't make me laugh son
of Chinese made junk. I would agree with a budget of $20,000USD I may well have bought a second hand machine to match and more likely exceed what I have made....the only problem is the machine
would be in the UK or US or somewhere other than New Zealand.
I value a hobby 'on what you learn in its pursuit'. In this regard CNC has been a very VERY good hobby indeed, I've had to learn about all sorts of subjects and had to learn new skills in order to do it.
The question might reasonably be asked 'does the $30,000NZD you've spent stack up against what you have learnt and the value you've gotten'. That is a tougher question, but one I think I can answer
positively, aside from anything else I have a machine that gets one, maybe two hours of use every day for my business.
Anyway, and more to the point, I've actually built something, solid and real and making chips right now.
Craig
Hi peteeng,
I've not investigated what is available locally. I note in one of your posts you claimed that Bunnings had a suitable product for our purposes,Hi Craig - I think grout is the better bet then EG, so what grouts can you get? Lanko 701 ? any sika products? Peter
sika grout 3200 in NZ E=38GPa model that
at that as Bunnings is in New Zealand also there is a high likelihood that it will available here also.
Craig
Hi TangentAudio,
That is a very sagacious comment.Maybe there's a sunk cost fallacy at play, and maybe it's foolish to keep throwing money at a project that will never be as good as something commercial. But making the most of what he has makes sense to me, since selling off his machine as-is or for parts isn't going to recoup his expenses. It's not like there's an option to turn his machine back into $30K so he can go buy a VMC. And living with it as-is may be fine, but will not scratch the "itch" he has to improve it.
Do I consider it a 'sunk cost'.......emmm, no I'm not sure I do. When I compare my machine to something like a Hass MiniMill then my machine will never be as rigid, but then my machine costs half, or less,
as much. 80% of the use my machine gets is making PCB's, for which its hugely overbuilt, and about another 15% in small parts in soft metals and/or plastics, again for which my machine is overbuilt.
Only about 5% of the time am I pushing the boundaries with regards to stiffness and size, and only at those times do I have to question the wisdom of building my own machine.
The second part about 'scratching the itch', then no purchase either new or secondhand would ever really succeed at satisfying my desire to design and build my own machine.
So depending on how you answer the first question, ie 'sunk cost' determines whether you proceed with improvements, 'throwing good money after bad', or ditch the whole thing as
a bad experiment.
I have answered the 'sunk cost' question by my actions. I've over the last five months or so invested thousands in parts and materials for a fourth axis and a trunnion fifth axis. I have started this thread with a view to
build a new headstock to replace then one I have. I have already got some very practical design types and costed them, if not exactly, certainly well enough to assist my decision making.
So I have never actually formally answered the question 'have I invested wisely, and should I continue?'.......but my actions have answered that for me.
Craig
Hi,
experimenting with grout with a Youngs Modulus of 30GPa. Looks like I need 40mm to 50mm walls (with the hollow pyramidal shape) to match the stiffness of steel or iron.
Ideally I would have a steel plate as a base, and another smaller plate at the nose, both say 20mm thick. This would allow for good bolting of the spindle to the nose,
and likewise be good bolting to the Z axis saddle at the base. Of course that also means that I can mill or otherwise skim the base and nose to be parallel to each other.
I would need to cast the grout in such a manner that it is anchored to both the base and the nose. I was thinking a ring of cap screw or hex bolts around the base and nose such that the grout
can form around the shank and head of the bolt to key it in tension. Does that sound like a similar technique that others have used?.
Craig
Hi Craig - Personally I would not cast the metal bits in-situ. I would epoxy bond them post cast. I would make it a solid block not hollow. Easier to mould and since its only 2300kg/m3 it won't weigh much. Mould in pockets for anchors or drill them. These can be threaded rods or steel bits welded to the back of the plates. But counterbored holes for bolts would be perfect I'd stay away from welding. The adhesive strength of the grout to steel is 2MPa see data sheet. Over time oils get down the interfaces and break it down so really the in-situ method is relying on mechanical fit-up not good for machines I feel. If you cast the headstock then epoxy in the plates and anchors a good epoxy will provide 30MPa of bond strength and its fluid tight so no breakdown... Its also better at impact strength then a concrete to steel bond. Chemset anchors outdo friction bolts in concrete and various bond strength tests show the concrete fails well before the bond does. Peter
https://youtu.be/LBe4okYOvyA not chemset but shows the result of a pull out test
Hi peteeng,
my idea was to partially drill and then tap the blind hole to install bolts such that the shank and bolt head were 'buried' in the casting by 50mm or so. Thus the steel plate
is 'keyed' into the grout solid and does not rely on adhesion. Also that the tensional stress transferred to the grout would largely be in the vicinity of the bolt head and
that is buried inside the grout solid.
One of the weaknesses of concrete, and I assume concrete like products, is that they are poor under tension. I am concerned that if I had as few as four bolts
epoxied into either pockets or bored holes in the grout casting that the tension on those bolts (retaining the spindle) threatens to 'rip them out by the roots'.
Second issue is that I would prefer the base and nose be faced by steel, or at least metal, so that I can mill and/or grind the surfaces flat and parallel to each other.
Also the metal facings, presuming they are thick enough would accept a thread deep enough to secure the spindle. The tension bearing capacities of metals
is well understood and much better than any concrete product I've ever heard of.
Craig
Hi TangentAudio,
No, I do not have a build log or a thread. I'm the sort of person who draws the plan of what it is AFTER I've built it. Naturally that does not work in situations where you have toMakes sense to me, Craig. By the way, do you have a build thread for your overall machine or your 4th axis/trunnion projects? Curious to see some photos.
instruct another person about what it is you want....but when I'm building I build what I want, and then....sometimes......get around to making a diagram to document it.
Craig
HI,
I have a string of things that I need to do, and hopefully will happen over a year or two.
I have a large servo motor, about 3kW, 12Nm cont 48Nm overload. It dates from the 90's. I don't know whether it new old stock or whether the manufacturer (Vickers)
re-built it, but its in perfect order. It has a resolver rather than an encoder and so what few drives that are available are really expensive. An ABB drive is about $3000USD,
thieving b********s! I'm building my own Field Oriented Control drive. Once its done I'll build/buy/steal a spindle, thinking BT30 Tool Change type.
You can see now why I want such a beefy headstock, because with this spindle in use I'll need it.
The project is:
1) Build the drive
2) Fit the servo, and get and mount an ATC spindle
3) Design and build a tool changer to suit.
Another project is to build a proper electrical cabinet. At the moment all the boards, drives and electronic bits are mounted on plastic breadboards which slide into a rack
underneath the machine. It works, but its not pretty. All the high voltage stuff is reasonably secure, I've not electrocuted any small children, neighbours, pets....yet.
Shame really, I can think of one neighbour who needs it!
A proper pro electrical cabinet to hold it all is nearly $1000NZD...and that's why I've not done it yet.
When I do THEN I'll have much better access to the coolant tank and pump underneath the machine but behind the electronics. You can get to it but its torturous. So cleaning out the swarf is a real pain.
I want a decent tank too, the current is about 12l, I want at least 100l. Needs a pull out tray to clear the swarf as well. I've got a dinky little 1hp three phase motor that would make an excellent variable speed
pump with a 750W VFD.
There's enough projects to keep me going for a while.
Craig
Hi Craig - Again I recommend not to in-situ bury the plates via bolts but to cast the grout part then epoxy the plates to the part. A 100x100mm epoxy bondline at 5MPa strength will support 5x100^2 = 50,000N or 5000kgf or 5T so technically you do not have to bury anything into the part. The face surfaces are good enough. I would though as insurance. My main worry is that a cast in faying surface has no actual strain transfer across the contact, only in compression. If you bond it with epoxy you transfer in tension and compression and you stop oil getting down into the interface. Once you add the buried bolts into the equation the failure loads become huge. Peter
Hi peteeng,
so your suggesting cast the grout with pocket, or bore after casting and then epoxy the plates to it?
Craig
Yes Craig. Pockets or holes for bolts can be timber dowels that get drilled out after casting... The granite machine builders have to epoxy in all there hardpoints....Peter
If you need mineral castings.You can contact me, my email
I'm from China,My company has produced a lot of products, small can reach 100KG, large can do 46 tons.
My English is very average and I don't know how to upload photos. Very reason to share my product with you.
https://grabcad.com/library/drone-cnc-diy-1