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Old Jun 24, 2012, 02:20 AM
I hate propellors
emufingers's Avatar
Australia, SA, Normanville
Joined May 2009
381 Posts
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Slightly out of left filed desin for CNC rouer for RC gliderbuilduing

After lots of reading in this and other forums I have come up with a proposal for a CNC rot specifically designed for RC modelling of the sort I want to do.. This for cutting pods and moulds for sing parts and fuselages up to 1.2 metres in length and a wing chord up to 250mm. The maximum height of parts will be 50mm.
I want the router to be cheap to construct but fiercely rigid. I want to used steppers in the 380-430oz in range and switch between using a dremel and a Ύ hp speed controlled router for cutting. The hardest material to be used will be corian type acrylics. I have plenty of room along a wall so a long narrow design suits my need.
I have read all of the comment about Joe and Solsylva designs and the cheap kits and light weight routers and notice that all of the have their p and strengths. I have also noted that in a machine with at least one long axis that rails and bearings and ball screws get very expensive. An issue with mobile gantry machines is that rigidity comes at a price. I am possibly too poor to even be starting a project, but I have come up with a design that I can afford, but it is a bit unusual. I know it won’t be a high production large footprint commercial machine, but I hope that it will be very good for my purposes.
Here is the basis of the design
• Fixed gantry
• Skate bearings to support and align a moving table with a travel of 1.2m
• Additional skate bearings on the gantry to hold the table down across the line of the router
• Moving table driven by a stepper mounted to the gantry and a rod supported by bearings driving two sprockets which will drive chains fixed to the bottom of the moving table.
• Y and Z axes are standard acme rods with steppers fitted to the gantry.
The aim is
• Support close to the cutting point to provide maximum stiffness.
• Minimise the length of wiring
• Provide a dust clearing channel across the gantry.
Gantry will be RHS steel 50*50*3mm thick walls It will be braced across both sides with 6mm aluminium sheet
The x axis rails will be RHS steel 50*50*3mm thick walls 1.8 metres long.
The moving table will be 1.5m long and 450mm wide reinforced at the edges with angle steel 50*50*3mm
Tell me if I am mad or have made any classic blunders. I have tried to keep the specs brief so let me kno if they need clarification. I am in the process of drawing the three d of the design in Sketchup.
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Old Jun 24, 2012, 02:38 AM
Registered User
Denver, CO
Joined Dec 2005
6,317 Posts
The moving table is best for smaller machines. To do it on a long machine the center support must be very rigid, to balance the weight hanging off to one side. Or you'll have to design some means of supporting the table. With a moving gantry you can make the table very heavy to help absorb vibration.
Mixing steel, and aluminum can cause corrosion, so will need to be protected.
Try to design it so the moving parts can be covered. Once you see how much of a mess some materials make, you'll know why.
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Old Jul 06, 2012, 09:39 AM
low tech high tech
vtdiy's Avatar
Southern Vermont
Joined Feb 2007
3,028 Posts
Quote:
Originally Posted by Roto Rob View Post
The moving table is best for smaller machines. To do it on a long machine the center support must be very rigid, to balance the weight hanging off to one side. Or you'll have to design some means of supporting the table. With a moving gantry you can make the table very heavy to help absorb vibration.
Mixing steel, and aluminum can cause corrosion, so will need to be protected.
Try to design it so the moving parts can be covered. Once you see how much of a mess some materials make, you'll know why.
Mixing steel and aluminum would be a problem if you located it in the ocean.

Gosh, watch out for stepper motors with aluminum, steel, and copper in their construction, and be sure to stock up on aluminum bolts, lead screws, rod, and bearings if you use aluminum in the structure.

emufingers I think your idea is workable, but actual specific design will determine its cost, and accuracy. You say you have the lengthwise space, and if you build it on a workbench, the sliding table can certainly be supported by bearings on the bench.

The table can certainly be made light enough with sufficient rigidity for 430 oz-in steppers, considering the weight of the material you plan to mill, but optimizing drivetrain design is important to speed, as is reducing table weight.

Accuracy of a moving table is dependent on the bearing rail on the moving table, just as accuracy of a moving gantry is dependent on the bearing rail (or ways) on the stand. The moving table has the advantage that bearing supports can be a greater distance apart. The disadvantage is footprint. But you have that covered.

btw, moving table machines include CNC Bridgeport mills, so it's not the province of only small or light duty machines.
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