# General questions about CNC routers / options



## MakingDust (Aug 31, 2012)

Hi. I am considering purchasing a CNC router to build custom cases. I don't know much about CNC routers as I have never used one but I have done as much research as I can but still have some questions. 

I will be cutting 3/4" baltic birch as the thickest wood. Mostly I will be cutting 3/8" birch plywood with a fiberglass laminate on it (4x8 sheet). Basically cutting squares and rectangles (nothing complicated). 

Questions
1. Vacuum Hold down? Do I need one or will the material be heavy enough to require this. Also I will be cutting foam wich is not heavy will the vacuum hold down help with this. 

2. Pneumatic drill. I only need to make basic cuts and drill all one size hole. I have seen that a lot of routers can also have a pneumatic or electric drill that sits next to the spindle as an option. I would like to avoid the cost of a bit changer.

Thanks for your replies

Andrew


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## jw2170 (Jan 24, 2008)

Welcome to the forum, Andrew.


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## malb (Sep 15, 2008)

Hi Andrew,
I work with an 8x6 sheet capable 14 tool machine in Australia. We are doing basicly similar things, but we cut mainly melamine particle board and prefinished MDF sheets for kitchen carcasses and door, plus some basic ply, plastic and aluminum.

We have one diamond tool mounted which we use for cutting 1.5inch particleboard benchtop substrates, and the rest are a variety of carbide tipped profile bits and solid carbide spiral drill and boring bits, used for all tasks as required.

In our instance, we are dealing with drilling multiple hole sizes (screw pilots, shelf pins, handle fixings, two sizes of hinge pilot for euro style hinges, and recesses for the body and pin of cam connectors). We also through cut components, and recess cups for euro hinges with solid carbide compression bits, and cut rebates and thin stock for benchtop templates with solid carbide down spiral bits, and mount a 2inch 3 flute diamond bit for skimming the spoilboard on a regular basis.

Our machine has two 10HP blowers for the vacuum bed, and a third for dust extraction at the cutter head through a foot setup.

With the vac bed, we can rapid cycle the machine. When it finishes cutting a sheet, the gantry returns to the origin and drops a scraper bar to 1mm above spoilboard level, then returns to the far end of the table sliding the cut sheet of the table onto an 'outbench' and retracts the scraper, while we blow any residue off the vac table. Once this is done, I load the sheet command file (g code) for the next sheet, and while the system processes that, I manually load the next physical sheet onto the vac table, check the proccessed file for obvious issues, turn on the vac/extractors and hit the go button. Typical turn around time (finish cutting 1 sheet to start next) is around 2 minutes. While the second sheet is cutting, I am labelling components from the first sheet, clearing the outfeed bench, and feeding material through the edgebander and stacking/racking finished components.

In that sort of environment (rapid sheet turn around, through cutting of reasonable thin sheet, and auto slide off) a vac bed is really the only way to go. It locks the full sheet into position, and will keep everything in place provided parts are at least 6in x 4in in size, and doesn't result in no go areas on a sheet due to the need to mechanically clamp sheets. We can also retain useable offcuts and reproccess them to usable components at any stage, or load overlength material overhanging onto the outfeed bench to avoid having to break this material down to do finished cuts.

I haven't cut fibreglass clad material on this machine, but suspect that it would be rough on the carbide tooling, and a step up to diamond might be required for reasonable tool life. We typically cut about 150 8x6 moisture resistant melamine coated partical board sheets and 60 precoated MDF sheets between changes with our solid carbide compression (primary cutting) bit, and get about a year from our drills and boring bits, and a lot longer from the profile bits as the don't get a huge amount of use.

Hope this helps you.


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## Iceman567 (Apr 29, 2012)

Hi Andrew, I own a small CNC (Shark) and have found two Forums that have plenty of CNC information Let's Talk ShopBot - Powered by vBulletin and Vectric Vectric Forum • Index page which makes CNC software. Besides the help you'll get here, I'm sure you'll get plenty on those two forums also.

Good luck.


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## fixtureman (Jul 5, 2012)

I own a 4X8 shopbot and it can handle what you want with ease. What size holes do you need to drill? You can drill and cut with a router. Also shopbot has a air drill setup for them.


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## tooler2 (Aug 11, 2012)

malb said:


> Hi Andrew,
> I work with an 8x6 sheet capable 14 tool machine in Australia. We are doing basicly similar things, but we cut mainly melamine particle board and prefinished MDF sheets for kitchen carcasses and door, plus some basic ply, plastic and aluminum.
> .


I always wanted to know on a vacuum table what is the surface that allows the vacuum through, and how do you keep it from filling with sawdust? Also, can you put a small piece on the table without blocking the rest of the surface?
Thanks, Rob


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## fixtureman (Jul 5, 2012)

I use a ULMDF spoil board on my table. Here is how I built my table. Base 3/4 plywood then 3/4 MDF glued down with 4 grids cut in for my vacuum and sealed. Then on top of that I have a sheet of ULMDF that I surfaced one side and then flipped it over and glued it to the vacuum grid being careful not to get the glue only on the high spots on the grid. I put about 400LBs of weight on it and started my vacuums till the glue set up. I then surfaced the top of it and I am good to go. The vacuum sucks right through the ULMDF and with 4 zones I only have to cover small sections if I cut small pieces. ULMDF stands for Ultra lite MDF You can use reg. MDF but the air doesn't flow through it as good.


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## tooler2 (Aug 11, 2012)

thanks
Rob


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## bgriggs (Nov 26, 2008)

One point no one has made is about the material you plan to use. 3/4" Baltic birch comes in 5'x5' pieces. You will need a machine with at least 5' of cutting area to deal with these. The typical 4'x8' machine would not have the travel to deal with this.

Vacuum table is the way to go.

Bill


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## malb (Sep 15, 2008)

tooler2 said:


> I always wanted to know on a vacuum table what is the surface that allows the vacuum through, and how do you keep it from filling with sawdust? Also, can you put a small piece on the table without blocking the rest of the surface?
> Thanks, Rob


As mentioned in original my post, I work with an 8 x 6 multitool system with 2 10HP blowers for the vac bed. These are plumbed into 4 off 4x3 styrene 'waffle boards' permanently mounted on the aluminium base of the machine. Waffles are about 1.3 inch deep, with grooves in x and y directions about 3/4 wide and deep, leaving raised lands about 4 inches square. This is all a permanent part of the machine.

For a spoilboard, we use stand 8x6 sheets of 5/8in MDF. This is not normally porous through the faces, but this is not an issue as we skim the skin of the top off each new sheet then flip the sheet so the skimmed face rests on the waffle board, and skim the other side which is now on top. Each skim pass takes nominally 0.5mm of the sheet thickness, and occasionally if a board is not totally flat we might need to take a third cut to prepare a new sheet, generally on the first side before flipping.

With the degree of vac we can pull through the skimmed MDF, the machine will anchor sheet offcuts larger than about 24x24 inches, smaller boards might get pushed around the table due to the thrust of the bit during cutting. However if we need to get something from an a smaller offcut, we can suround the offcutt with bolster parts (offcuts about 12in wide and whatever length is at hand) to lock the offcut in position. The bolsters provide physical stops to prevent the offcut sliding, and are not needed to avoid vacuum leaks through the unused areas of the spoilboard.

As mentioned in my original post, the system can cut parts down to about 6in x 4in safely, smaller than that there is a danger that the extractor foot around the router bit will grip the part and lift it out of the full sheet skeleton after cutting it. This is not nice as the bit can hit the component and hurl it accross the factory (like kickback on a table saw). There is enough vac on the table and through the spoilboard to overcome bows of more than 1/4in on a sheet if we have to, but we prefer to position the sheet so the raised part is in the middle rather than the ends of the sheet to minimise chances of vacuum leakage once we cut through the sheet.

With the skimming process, we have two skim routines, new sheet and existing sheet.
With a new sheet, we use the new sheet routine for the first skim. This resets the tool zero depth for all tools to 15.5mm above the waffle board and skims the board to that height. The existing board routine drops the tool zero depth 0.5mm below it's current level and skims the board to that level. For through cutting and through drilling, we just cut into the spoilboard, (around 0.1mm) so the board gets scarred. We reskim each morning on setup, and occasionally during the coarse of the day if the surface is getting ragged or small parts start to move in the skeleton. Typically we can get 10 working days from a $20 spoilboard.

The unit also runs another 10HP blower for the dust extractor, working through a foot surrounding the bit. This generally clears up about 98% of the waste produced, and we blow the surface of the spoilboard with compressed air between sheets to ensure that no dust remains to facilitate sheet movement. dust being sucked into the MDF core is not an issue.

Hope this helps you understand how this works.


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## tooler2 (Aug 11, 2012)

Excellent explanation, thank-you for taking the time to reply in detail. When you are working on less than full sheets how do you find the piece's home (0x, 0y)?
Rob


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## malb (Sep 15, 2008)

tooler2 said:


> When you are working on less than full sheets how do you find the piece's home (0x, 0y)?
> Rob


I failed to mention that the machine has air retractable stops along one end and one side that pop up while it is not cutting. We norrmally load full sheets tight against these stops, which positions the sheet accurately. The system logic retracts the stops as soon as the vacuum bed is powered.

The corner of the spoilboard nearest the z axis depth zeroing target is the nominal 0,0 for the table, so we normally just place offcuts flush with the end and side of the spoilboard, lining up by touch. Alternatively, we might set some bolster offcuts around a small offcut to be cut, then relocate the cutting path so it co-insides with the offcut in software.

For critical things (offcut just larger than the bit we need to get out of it) we will run the program without the sheet on the table to leave a tool trace in the spoilboard, then position the offcut to completely obscure the tool trace, or to allow an even trace exposure around the offcut. We don't go to that level all that often, but occasionally we need to get a drawer front or something similar out of an offcut where buying a new full sheet might cost $300+, and the component would use 5% of the sheet, leaving the rest in stock maybe forever. In these circumstances it becomes worthwhile to stuff around for a bit to save in the long run.


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## fixtureman (Jul 5, 2012)

therouterlady said:


> Hi Andrew,
> 
> The material is already heavy enough, you do not need vacuum table.
> And the drill is not needed either. this will add up the cost a lot.


I don't know what they are talking about but I run 3 different machines and all of them have vacuum on them. I cut some real heavy material in the 250 LB range and still need vacuum to hold it in place.


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## tooler2 (Aug 11, 2012)

malb said:


> For critical things (offcut just larger than the bit we need to get out of it) we will run the program without the sheet on the table to leave a tool trace in the spoilboard, then position the offcut to completely obscure the tool trace,


Very clever! My experience in cnc is with milling machines, working to .0002'' so set up is rather more intense. How do you set the z axis ''0'' after a tool change without re skimming the whole table? How long would it take to re skim?
Thanks, Rob


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## fixtureman (Jul 5, 2012)

If I need to be exact on a cut I place the piece on the able and cover it with news print and throw a plotter pen in the collet and run a profile so I can see how much I have to offset my cut.


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## kolias (Dec 26, 2008)

Besides the machine you will also need the software (CAD / CAM) to run the machine.

They can add a lot to the cost and the learning curve

Vacuum will be good for a commercial environment


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## hitechengineering (Sep 12, 2012)

*Hi*

I am new this forum and hope I enjoy being here and resolve issues as and when they occur.

Hoping your humble support!

Regards
James.


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## chinalimac (Sep 17, 2012)

*cnc router*



MakingDust said:


> Hi. I am considering purchasing a CNC router to build custom cases. I don't know much about CNC routers as I have never used one but I have done as much research as I can but still have some questions.
> 
> I will be cutting 3/4" baltic birch as the thickest wood. Mostly I will be cutting 3/8" birch plywood with a fiberglass laminate on it (4x8 sheet). Basically cutting squares and rectangles (nothing complicated).
> 
> ...


I think a T-slot table will be enough to clamp the thick materials as yours. Also the tool changer or drilling head is not necessary, a drilling head is even more expensive than tool chnager.


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## malb (Sep 15, 2008)

tooler2 said:


> Very clever! My experience in cnc is with milling machines, working to .0002'' so set up is rather more intense. How do you set the z axis ''0'' after a tool change without re skimming the whole table? How long would it take to re skim?
> Thanks, Rob


The machine is a 14 tool unit, in a typical program for melamine carcass components, we sequence through about 3 or 4 tools normally, 3mm screw pilot drill, 5 mm shelf pin drill, (maybe 8mm down spiral if a rebate is needed) and 3/8 in compression for parts cut out. For colourboard doors and faces, we might use a few more, 8mm and 10mm drill for hinge pilots, 8mm and 20mm for cam fasteners, hinge cups are cut to 12 or 12.5mm depth from top surface with the 3/8th comp cutter.

The system has software routines to individually sense (detect) z zero for each tool and store them. We can access these setting and edit them to 4 decimal places in millimetres via keyboard or adjust in 0.1mm steps via console push buttons. 

We sense key tools (3mm and 5mm drills and 8mm and 3/8in cutters and 50mm diamond skimmer) daily when starting up the machine, skim the board, and run test cut routines to check penetration into spoilboard (aiming for about 0.1mm but set by eye or running a finger over the tool trace on the board) and manually tweak to suit, then save these settings. Other tools are sensed and test run before undertaking a sheet that needs them, things like the 20mm cam fastener body borer, 3/8 single flute plastic cutter, or 45 deg V groover are used probably once a week so we sense them just before we need them, then make test cuts and mike them and tweak settings to obtain required settings.

The system automatically translates these sensed values to absolute tool depths by making allowances for the spoilboard thickness as it varies with skims (max 15mm new board down to 3mm minimum in .5mm skims).

If we need to replace a worn or damaged tool betwen sheets, we initiate a depth sense for that tool afterwards, then run a test pass to check penetration and tweak as required, then save the new setting and continue cutting.

Homing the machine at start up, sensing four tools, skimming and testing the drills and cutters takes about 10minutes at the start of the day. A reskim takes about 3 minutes, and retesting drill and cutter depths takes about 3 minutes for the base set, but is rarely required after a reskim.


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## chinalimac (Sep 17, 2012)

Hi Andrew, for 3/4'' birch wood, a TD-slot clamp table is enough for your use. Also you do not need the drill head beside the router head, as the router itself can do the drilling as well, only you need to use a small bit. 
If you need any information on this, feel free to contact me. 

Mary


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## StevePixley (Aug 10, 2012)

Why is a CNC router better than a manually operated one?


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## malb (Sep 15, 2008)

StevePixley said:


> Why is a CNC router better than a manually operated one?


Sometimes they aren't, sometimes they are, it depends on what you are trying to do, and how many you want to do.

In my job, I am cutting sheet for custom kitchens. The manager measures the area for the kitchen to get overall dimmensions accurate to 1/16 in or better, establishes customer requirements and prepares a 3D computer design model for them, to the point of having face panels etc the correct colours. The design model is presented to the customer, and any changes required ae made. The project is then fully costed, and further changes made if needed for cost reasons. 

The design is then computer processed to convert the 3D design into a layout of the minimum possible number of sheets (8ft x 6 ft) of material, incorporating all holes etc required for assembly screws, hinge and drawer slide screws, shelf support pin holes, hinge recesses in doors, other hardware etc. The sheet layouts are saved to computer for later access by the CNC router. The computer also prints labels for the parts in the job, to identify each component in the job (there may be 300-500). 

When I start to cut the job on the CNC, I load a full sheet, and the corresponding computer file, do a final check for layout errors, and fire up the router. Depending on the sheet complexity, a sheet can produce between 1 and about 70 components, and the machine can do all of the cutting, drilling, boring etc for these components in between 1 and 18 minutes. Cutting the same set of components on a panel saw normally takes as long or longer, and then the cut blanks need to be drilled etc. 

In other production instances, something might be designed once and cut hundreds of times. Using a CNC ensures that each of the parts is as good as the original, ie there is no dimensional variation over the parts run.

Some people use a CNC to route signs, where the number and of size of characters vary, but the overall outline may be fixed. Without CNC, you are limited to the fonts and sizes of letter templates on hand, with CNC and basic design software, you have access to all graphics, fonts and sizes available on the design computer, you can do a basic layout and refine it on screen, then convert to machine instructions, save the file, and cut the sign. Others use similar software to produce photo realistic images in wood or other material, which could only be done by hand carving otherwise.

On the other hand for simple one off jobs, a handheld or table mounted router and a skilled operator can be quicker and more efficient by eliminating the computer side of the equation.


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## Tool Home LLC (Sep 18, 2012)

StevePixley said:


> Why is a CNC router better than a manually operated one?


In addition to what Mal noted, with a CNC machine, you can make moves that would be virtually impossible to make accurately otherwise. Think about simultaneously moving the turning bit in 3 axes, or 4 axes.

You can carve.


Tom


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## fixtureman (Jul 5, 2012)

Also if you have 100 of the same item to cut a CNC will cut every one exactly the same and faster. I use a hand router at work to cut out parts and will go through 3 bits for the same number of parts as my CNC will using only 1


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