Hi Everyone - Newbie wanting to create model boat hull plugs

[g6swj]

Hi Everyone I would like to introduce myself - I am Jonathan, based in Northamptonshire and I am currently in the market for a CnC router - I think!

I understand steppers and how to drive them and that's about it.

I am not sure if I can make this reality or if what I am after will be out of my budget/justification of the amount of intended use

I have recently been in "sponge" mode soaking up as much info as I can - the pandemic might have worked in my favour as it's stopped any knee jerk purchases from eBay etc that could have turned out to be a poorly thought out approach.

So I want to mill modelling foam to create the type of thing in the picture below which can then be used top vreate a GRP plug - I think I will need a 4th axis?

Ideally I would like to be able to cut from a solid block of foam approx 1500m x 500mm x 400mm (Z) I realise this probably not possibole without ££££££ and I think I may have to cut in sections and join them together.

Last night I pretty much gave up on the idea as too complex, as my brain was addled with info and machines costing £££££ , too far out of my comfort zone - so I am posting here for any pointers that might be able to put a smile back on my face and a dent in my wallet.

I have £1.5-2k to spend

I was tempted to buy a cheapo £100'ish China derived machine which would end up in the skip just to get on learning the software (Mach 3) and g code - would this make sense - any suggestions as to ideal platform - or any other suggestions to get on with the learning wqould be much appreciated.


https://modelboatmayhemimages.co.uk/images/2021/01/24/2021-01-24_12-26-50.png

https://modelboatmayhemimages.co.uk/images/2021/01/24/2021-01-24_12-27-05.png

many thanks for all and advice in advance
Regards
Jonathan

[JAZZCNC]

Hi Jonathan,

Well, this is certainly doable if you increase your budget by at least 50%. With £2k you will really struggle £3-4k will be a more realistic figure, even then you will have to buy wise and have a good knowledge of using steel material, forget using an aluminum profile, this alone would eat your budget.

I think you'll find the best design in terms of the cost would be to fasten the block of foam to a fixed rotary head and then have the gantry travel on a frame above with spindle moving up/down in Z while the block rotates below just like a typical 4th axis setup.
The reason for this design is because it will make the Cam side so much simpler, you can use standard wrap Cam features for tool-paths. Using a design with the spindle rotating on the Z-axis I think will mean you need 5 Axis tool-paths and this gets expensive quickly and complex.

Hope this helps and good luck

[g6swj]

Hi JAZZCNC,

Thank you for the information - if I dig deep and find £4k is what you envision a custom build or an off the shelf offering?

Interested to know more - Really appreciate your time posting information...

Regards
Jonathan

[JAZZCNC]

Hi JAZZCNC,

Thank you for the information - if I dig deep and find £4k is what you envision a custom build or an off the shelf offering?

Interested to know more - Really appreciate your time posting information...

Regards
Jonathan

Those figures I gave were for a DIY build and you won't find this size and type of machine on any shelf so it will always be a custom build.

To give a more accurate price to build something like this would require a more definite design so it can be costed correctly, if you are looking to have it made then drop me a PM and I will discuss it in more detail and give you a fixed price.

[routerdriver]

If you want to do it in the same manner as the illustration you definitely need a five axis machine.If you try to do it with a three axis machine,there will be a point where you can't achieve the depth with a vertical spindle.The bad news is that the software alone for a five axis machine might have to have a custom post processor and will utterly demolish your budget before you even get a machine through the workshop door.Presumably you have some experience in determining pull direction for mouldings and location of split lines and these factors can make life difficult.For a simple hull shape with no undercuts,it is quite possible to break down the plug into bite size chunks that can be cut to shape on a three axis machine and then bonded together.Which means the cost of machine and software can descend into the realms of the dedicated hobbyist.Its also worth keeping in mind that even the slabs that make up each layer can be broken down to fit a smaller machine and then bonded together prior to gluing the stack together.

The whole project raises question after question but be assured that it is definitely do-able.It does need a certain level of facility with 3D modelling to begin with and its well worth trying as many trial versions of both CAD and CAM software as you can get hold of.I would caution that with a hobby level machine and a desire for a detailed surface it can take quite a while to machine the whole of the surface and even then it will require a fair bit of hand finishing.

[m_c]

The big issue with 5 axis is the CAM, and post processor.

There are a few 5-axis machines running Dynomotion KFlop's and KMotionCNC can be configured to handle gimble heads/trunnion tables, but I have no idea how the users are generating the code.
I can't find any specific threads and don't have time to trawl through them, but I'd suggest doing some searches on Dynomotion's own forum ( https://dynomotion.com/forum/ ), and the Dynomotion board on CNCZone ( https://www.cnczone.com/forums/dynomotion-kflop-kanalog/ ) for "kinematics" and "RTCP" which should throw up some of the 5 axis machines.

I suspect most will be using Fusion360 for CAM, but you'll need to pay for the full version to get more than 3-axis machining.

[g6swj]

Thank you all for the information - a lot to digest - some more pieces of the jigsaw begin to fall into place

Regards
Jonathan

[routerdriver]

I don't think a trunnion table would be practical with a model 1500mm long and with those overhangs on the stern.Breaking the model into a number of sections to be assembled is certainly a possibility,should one have the experience of 3D modelling.Its worth keeping in mind that the machining can be used to create holes for dowels that may be used to align sections and the same sort of techniques that bricklayers use to cover joints with the next block above can also be used to help alignment and reinforce the joint.

The 400mm Z is the killer as few hobby level machines will have any hope of getting near this height and even if they could,you can't get down the side of a tall block because the motor body and backplate are likely to foul.A fourth axis might help with some aspects provided the blank has sufficient rigidity to resist the combined forces of gravity and machining-but where do you find a machine with a 400mm Z axis?You would need rails with a length of 900mm for the Z,about 1100mm for the Y and 1800mm for the X so you would need a fair amount of workshop space.

Personally,unless the machine building challenge is as important as the creation of the model,I'd be looking on Ebay for something with a 600X400X70 envelope and extending my modelling skills.Then I'd be running as many machining simulations as possible so that when I wanted to produce something I could be confident that the parts I wanted would be coming off the machine.

On a different note,I would be curious about where you find models of boat hulls with that much detail as it looks very professional.Any hobbyist capable of that level of surfacing and detail has already covered a lot of the ground.