[BradN]

Hi guys,

Hopefully it's okay to ask for help in this section.

I'm looking to build a machine with a working area of 1.2m x 2-2.5 m, to be used mainly to cut molds and other odd jobs related to the marine / yachting areas. It will need to cut out foam or wood, If possible, Aluminium would also be great (At a very very slow rate).

Is it okay to use 20mm linear rails or would 25mm be beneficial? They are pretty close in price, probably HIWIN at this stage from Alibaba.

Will the motors need to be Nema 34 for a machine this large? The Gantry will be aluminium so not too heavy. Do any cheap-ish low inductance motors exist? have trolled ebay and alibaba with no luck. Motor drivers at this stage Gecko unless anyone has another recommendation.

I have bought a nice C3 Z axis screw (275mm travel) but the end plate suggests it is suited for a smaller motor, Is it okay to use a smaller motor here and use the larger motors for the other Axis's?

Thanks!

~B

[pippin88]

15mm profile rails (such as Hiwin) would be enough, you won't exceed the rated loads with what you are planning. 20mm rails may be easier due to bigger mounting bolts. They are also taller which may be good if you want a ballscrew alongside, but it's best to minimise overhang etc where possible.

I've had good experience with BST automation on Aliexpress. You want medium (not light or zero) preload ideally and consider getting high precision (rather than standard) which is available if you ask for it.
Most sellers will customise orders and lengths to exactly what you need, so don't be constrained by why they have listed.
For ballscrews you want high lead (10mm per turn or greater). If you are doing mostly wood and particularly foam, I'd suggest 15-20mm lead ballscrews. I recently got some SFE1616 screws from BST and the quality appears quite good (better finish than the classic RM1605 Chinese ballscrews) though I haven't got my machine moving yet.

[ger21]

Agree with the above. 25mm rails will provide zero benefit in your case. 20mm are more than adequate.

Will the motors need to be Nema 34 for a machine this large?

Size really has little to do with motor selection. Motors should be chosen that will meet your performance goals.
Motors also need to be a good match for the drive system. Are you using rack and pinion, or ballscrew?
Also keep in mind that there are many different Nema 34 motors. Bigger is not always better, as a medium size motor (~600-900oz-in) will often outperform a larger motor. Drive system plays a large role here.

[wizard]

That is a fairly large machine, one thing that I'd like to point out is that you should consider AC servos over steppers. The price can be acceptable though they are a bit more expensive that steppers. This should allow you to archive a wider range of axis velocities while avoiding high lead lead screws. The problem as I see it is that you may be expecting or need a wide array of accuracy. Molds for fiberglass layup likely being the loose end of the tolerance game and machining aluminum the tight end.

Given that I'm not sure it makes sense to build a single machine for such a wide array of materials, especially one this big. So what sort of aluminum parts are we talking about here? If it is anything more that low tolerance light sheet metal work I'd reconsider building the machine to support machining of aluminum. Let's face it if foam is a primary goal you can build a very light weight machine relatively cheaply. Any significant amount of aluminum machining would require a stiffer machine and most likely much higher accuracy. The other thing here is when I think of boat making and foam I often see large 3D structures requiring very tall Z axis support. A tall Z axis really works against you when trying to do aluminum and even wood on a low end machine. You didn't mention your Z requirements so I brought this up due to little in the marine world being flat.

So there are some questions you need to ask yourself.
1. What is the real Z axis requirement to make the molds you intend to make? This is real important because I tend to think of marine molding as very 3D. It isn't unrealistic to have a meter or more of Z travel to do foam work for marine molds.
2. What are your expectations for Aluminum? Producing a machine this size to machine anything more than thin sheet metal means a machine largely overbuilt for machining foam. Plus machining metals with anything more than trivial parts requires a coolant/lube that makes a mess
3. Also consider that volume machining of sheet metals can be less than ideal on a router. It may pay to have such work done by a water jet contractor or somebody with a laser.


Obviously you know what your goals and needs are here. I just had a few alarm bells go off when I read about molds for marine work.

[victorofga]

I believe for foam you need a definitely larger at least 1.50x3.00 meter..
and for aluparts you need a smaller what stronger enough to handling the metal..

for foam you can go with the supported round rail.. due the cutting force wont be high
nema 34 probably sufficient...
Z movement somewhere 12-16 inch.. 30-50 cm...
while you can work with """slices""" ,,, a lot simpler to work ready a large block..

[BradN]

Thanks for the replies guys.
The jobs will be almost random. The large cutting area is to acommodate the standard 1.25 x 2.4m sheets which quite a few materials come as. The actual Z axis height shouldn't need to be too high as most of the work will be quite low e.g. Rudder and foil cores, spreader molds.

20mm Rails it is then

Wow that is a very high lead! Good to know as I was about to buy a low lead one.

Currently thinking Rack and Pinion for the X axis. At this stage from cncrouterparts. Ballscrew for the Y.

I was hoping aluminium molds for kite hydrofoils or similar but perhaps you are right Wizard and it should be left for wood and foam.

Has anyone bought from Kelinginc.net? they have 640 oz nema 34 motors for $89 each. I think Servo's might be a bit out of reach

[BradN]

The Z axis ballscrew arrived, the motor bracket is for a nema17 motor, is it okay to use a nema17 motor for the z axis? or get another bracket?

[wizard]

Thanks for the replies guys.
The jobs will be almost random. The large cutting area is to acommodate the standard 1.25 x 2.4m sheets which quite a few materials come as. The actual Z axis height shouldn't need to be too high as most of the work will be quite low e.g. Rudder and foil cores, spreader molds.

Like I said only you know what you are targeting. I just see the potential for a lot of Z axis need.

20mm Rails it is then

Wow that is a very high lead! Good to know as I was about to buy a low lead one.

Well do figure out the resolution you will get before going to a high lead screw. You need to have enough resolution to meet the requirements of your molds. Given that we are talking foam here for fiberglass boat parts I don't see a huge need for accuracy. However you should do the calculations to make sure you can get the required resolution and precision at the machine.

Currently thinking Rack and Pinion for the X axis. At this stage from cncrouterparts. Ballscrew for the Y.

Here is the thing, if the machine is limited to foam machining you actually have a lot of low cost options. Well relatively low cost options. A rack drive on the X and Y would be nice but so would a belt drive with heavy duty timing belts. It really comes down to how good the parts should look, I don't imagine a rudder being appearance focused. However if you are molding up furniture for the interior of the boat appearance could be very important thus forcing you to use a axis drive method that delivers higher quality results.

I was hoping aluminium molds for kite hydrofoils or similar but perhaps you are right Wizard and it should be left for wood and foam.

Actually I'm not sure what a kite hydrofoil is. However if it is something of any size at all you are not going to get a high quality mold out of a cheap router type machine. Also would you be molding something here with the gel coat first in the mold with the intention of it being visually appealing.

When thinking about wood we go back to having an even more robustly built machine. I don't see it as a problem to build a machine suitable for both wood and foam though. Trying to do work in aluminum just puts you in a different category machine in my mind. For one thing carving a large mold in aluminum would likely require a lube/coolant system. I suppose you could try dry machining the mold.

In the end it comes down to expectations, if the wood you machine is for fiberglass cores, you might not need the same quality results compared to machining woodwork for the boat.

Has anyone bought from Kelinginc.net? they have 640 oz nema 34 motors for $89 each. I think Servo's might be a bit out of reach

Servos can be somewhat more expensive but they are on the other hand cheaper than they ever have been in the past. Do make sure you include the costs of all parts to build a stepper based system including the power supllies. My thought with servos was that they would give you the velocity and resolution required for maching on a large machine.

[awerby]

A NEMA 17 motor is too small and weak for any but the smallest and lightest CNC machines. You'll want at least a NEMA 23 motor for your Z axis. Get another bracket, if you think this ballscrew assembly will work.