What is the size of your table ?
Zebra, I found your thread and will see what I can learn from it over the next few days. But you mention wanting to machine resin molds. Have you looked into Corian molds (can even do DIY slabs of it)? The RC fly boys seem to like it. Affordable, supposedly, and seems like they come out with good surface finish.
I am using a regular gantry / Z-axis design where the spindle moves up and down, not the gantry.
I hadn’t even considered the second option of moving the whole gantry bridge up and down. As for which would be more stable, I suspect there are too many variables for anyone to know for sure. I bet that either could be stable when built well with quality rigid materials and joints. Similarly, either could be unstable if designed poorly.
The only other design option I considered for the Z axis was to have the table move up and down instead of the spindle but I doubt it will get further than being a passing thought.
I have read up extensively on aluminum cutting speeds and spindle recommendations. That is the problem. There is a lot of self-proclaimed experts who offer conflicting advice. it’s hard to know who to listen to as everyone sounds like an expert when I know so little on the subject… they all claim to speak from experience too…
When faced with conflicting advice, I tend to try and guess by applying a little common sense and deductive reasoning. My current thought process is something along the lines of:
Professionals typically use CNC mills for metal-work. It is commonly stated that mills are more accurate for cutting metal. A lot of that is down to the more sturdy build quality on mills but, most mills are still equipped with lower speed motors. Specifically, motors that are capable of higher torque at lower speeds without gears. They all do a good job on cutting aluminum.
While you can use a router for cutting aluminum, I don’t often see it suggested that it is the optimal choice over a mill (although it is becoming a more mainstream use).
I am unlikely to be making more than one aluminum mold per week so speed is far less important that accuracy. I am more worried about ending up with a mold surface that requires a lot of additional smoothing and finishing work as this would be extremely difficult and time consuming for a hard aluminum alloy. It’s hard enough smoothing a gel coat layer in a mold cavity.
That sounds like I am leaning towards the milling head but it’s not that simple… there are also a lot of data-points where people are getting great results cutting aluminum quickly using 1.5kw or 2.2ky Chinese spindles and… apparently… higher spindle speeds make end mills last longer… or something. The higher speed option offers more versatility too.
You can see how I get myself confused…
The milling heads sold by little machine shop can be used on a regular or CNC mills. Being CNC or manual makes no difference to cutting speed capability of the spindle. They sell kits to convert their manual mills to CNC too.
Their milling heads are lower speed because that is optimal for cutting harder metals like steel (apparently). Their key selling point is that they can achieve their max torque at low rpm without gears. Apparently this makes them quieter. Their build also looks a lot more sturdy that most router spindles and everyone agrees that more sturdy = better results. It’s one of the few areas where there is some level of concencus.
There is probably no such thing as the ideal spindle speed for aluminum (or any other material). There are too many other variables. I would probably be able to achieve good results with either a milling head or a router spindle if my machine is built right and I select the right end mill. I’m going to do more research but I suspect I will find only that both have pros and cons. Either way, I see a bunch of trial and error in my future…
I think the ideal would be if I could afford to buy a bunch of options to be switched around depending on the job. It would be awesome to have a milling head, router spindle, 3D print extruder and plasma cutter option on the same machine! I can dream can’t I…
It will have a 36" x 12" x 8" cutting area. The rails I bought would allow a slightly wider Y axis but I don’t need it for what I do. I could make it up 36" x 24" with what I have though.
I plan to add a 4th rotational axis in the near future. I’m currently searching for the elusive reasonably (low) priced motor / lathe chuck / tail stock package that offers acceptable accuracy, enough capacity to hold the blank stocks I work on and acceptable build quality etc.
The 4th axis will run along the X-axis (the 36" one) to hold up to 30" slabs of blank stocks to work on.
It’s a small desktop machine in the scheme of things but, for some reason, reasonably priced desktop CNC machine with 30"+ of cutting space are as rare as Dodos.