Bespoke CNC

Hi all,

I manufacture aircraft propellers. The shape is machined from laminated lumps of beech by a company I sub-contract for the job. I've decided to purchase my own machine to bring this operation in-house. I've been looking around at 'off the shelf' machines but they don't seem to be so appropriate for very specific purpose and I will be buying a lot of features I won't use.

I need a very solidly built machine to minimise resonance with a working area of around 2.5 m x 250 mm and about 200 mm travel on the Z-axis.

I was tempted to design and build my own machine, the resources seem readily available and I have a mechanical/electrical background but I could easily spend all my time building and not getting on with production.

So....I'm looking for a company who can build me a machine to my specific specifications, nothing complicated about what I want, just sized and shaped for my application.

Any recommendations?

Thanks, Prop Man.

Prop Man,

Are all the propellers the same, who currently does the cad/cam

Just learning the software can take a long time, you would need 4 axis and the software would cost around £5K +

What is the tolerance on the props, how many do you need to make.

When/if you make them yourself and you screw up YOU PAY.

I'm sure a lot of peeps on here could make this, me included but don't know a dedicated company that makes them.

Phil

Thanks for your reply Phil. It is very unusual to make 2 propellers the same. We make 2-3 a week and business is growing. I design the propellers mathematically then I draw them using Rhino. Then I pass the 3D drawing and the lump of wood to the machinists. I have looked over the shoulder of the company doing my machining and the CAM software doesn't look that complicated, the sort of thing I'm sure I can learn. At the moment I am spending about £25K a year on machining, it certainly makes commercial sense to gain such capabilities as it is a major part of our manufacturing process.

I'll be happy with a tolerance of 0.2 mm.

At the moment they are being made on a large 3-axis Thermwood, which seems to do the job well but the job is taking about 6 hours per prop including programming. I believe the machining time can be speeded up considerably with better tooling and fixtures. The loads on the cutter are quite high and the tool has to be extended from the holder by about 150 mm in some cases to gain clearance from the work. I'm supposing that a 3-axis machine will have better rigidity at the spindle, for such big heavy cuts when roughing out, on a pretty hard wood. I'm looking for a 20 mm tool holder, again to help minimise resonance.

How do you think a 4th axis will help the job?

Keen to enter discussions with anyone with track record building large-ish machines who can take on this project.....

-Prop Man

Quote:

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Originally Posted by M250cnc

Prop Man,

Are all the propellers the same, who currently does the cad/cam

Just learning the software can take a long time, you would need 4 axis and the software would cost around £5K +

What is the tolerance on the props, how many do you need to make.

When/if you make them yourself and you screw up YOU PAY.

I'm sure a lot of peeps on here could make this, me included but don't know a dedicated company that makes them.

Phil

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Prop Man,

4th axis means a rotational axis, and it would seem to be impossible to do this without a rotary ?

Heavy cutting means potential for movement/deflection of the prop

Are they doing this with one cutter setup, this is where expensive software can cut down machining time as well

Maybe post a sample file to show the size/shape of what you are after

Phil

Phil,

Do you mean rotation of the work for the 4th axis? If so, the work is turned over manually. The propeller blades do suffer from resonance when the finishing cut is being performed on the second side as there is little material left. The work is held in the centre and at each end by the parent material, which is cut away once the process is finished. In addition, wooden wedges are jammed between the bed and the work, about half-way down the blade for the final cut on the second side to add rigidity and improve the finish.

I have some good ideas of how to build a much improved fixture system which allows the work to be well supported and rotated manually along it's long axis to machine the second side. Fixture building is something I will do as I have the capabilities and experience to do this.

They are roughing it with a 25 mm braised tipped square cutter and finishing with a replaceable HSS bladed cutter with a radius on the corners.

I'll try to work out how to put some pictures up. Propellers range from around 50" long to 95" long. The blank starts off as a square section and most of the material is removed during machining.

Prop Man

Pictures of the Thermwood cutting a propeller in the 'galery - albums' section.
-Prop Man.

It depends how much money you want to spend.

Due to the resonance/flex issues, I'd say a normal 4th axis isn't going to be much use, however a tilting table would be, as it would allow for faster maching. As instead of the existing method whereby a radius cutter works side to side the length of the prop, with a tilting table, a larger flat sided cutter can make several passes from root to top to provide a smoother profile. However, it will add alot of cost, and complexity to the machine.


I'm often surprised at the lack of companies offering bespoke machine building, but then there is the issue of who becomes liable when things don't work as intended, which means such companies would probably start charging an unaffordable premium to allow for having to redo things when they don't quite work as initially planned.

Quote:

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Originally Posted by m_c

It depends how much money you want to spend.

Due to the resonance/flex issues, I'd say a normal 4th axis isn't going to be much use, however a tilting table would be, as it would allow for faster maching. As instead of the existing method whereby a radius cutter works side to side the length of the prop, with a tilting table, a larger flat sided cutter can make several passes from root to top to provide a smoother profile. However, it will add alot of cost, and complexity to the machine.


I'm often surprised at the lack of companies offering bespoke machine building, but then there is the issue of who becomes liable when things don't work as intended, which means such companies would probably start charging an unaffordable premium to allow for having to redo things when they don't quite work as initially planned.

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Yes seeing how long it is i would agree the tilting table idea which as you say can cut down the machining time which was my thinking.

But wow the cost factor of a 2.5 Mtr tilting table, maybe its all you need to add to a standard machine.

Phil

Haven't checked out the pics yet but could you not still manually turn the piece for each side but add tabs on the blade edges? it would stay rigid in the block then. These have to be cleaned up anyway to balance the prop. I would go with a KISS approach my self?

Thing with bespoke machinery is that A) frequently the cost would be prohibitive, and B) if you go to sell it in a few years to upgrade, it may not easily sell (unless you sell it to a company doing the same kind of work).

You sending orders direct on Rhino / CAD / CAM?

With one-off jobs, 40% of your time can be on set ups (clamping / clocking / changing cutters etc). Bear in mind with wood you can't use coolants, so feeds and speeds can't be ramped up quite so high as on other jobs, and along with that, there is the issue of tool wear as well, and that'll be high.

How are they programming the machine? Directly from CADCAM, or G-code from the control panel?

Props certainly don't strike as an easy job, so 6 hours per job sounds like a pretty good time from here, but I haven't seen the job being done.

I would think these are valuable skills to be in house and thinking of a bigger unit the costs could be covered in the first year. Your limits would not just be props either but i'm sure you have thought of that. For what your costs are at the moment you could probable invest in a secondhand machine and save on build time. For the size of machine you need in length as long as you have the space a much more prudent machine should be considered. If you say business in this area is picking up then time factor is a large cost you need to reduce, this could offset some of the cost outlay?

You could even consider something like this? http://cgi.ebay.co.uk/CNC-ROUTER-ENG...item4a9ff4978a

Other points to remember if you bring machining in house is that whatever machine/s you have, it / they have to earn their keep: if you suddenly have a quiet period, have you got other work you can put on the machine? If not, it could suddenly become an expensive liability; you'll still have rent / rates to pay on the workshop space (have you a workshop at present, or are you working on the designs at home?) , service supplies for it (electric / heating / air / water, dust extraction and waste disposal charges), materials, labour (your biggest cost), equipment costs (machine itself has to be paid for, tooling, clamping / fixture systems, maintenance of machinery, gauges and test gear) - these all have to be paid whether the work is there or not.

Bear in mind also that if you don't know how to use / run that machine, you need to employ someone that does, otherwise you make nothing at all and you end up with customers frustrated with delays (they themselves may have customers waiting for a finished item) whilst you figure the machine out - it's not impossible that a customer ends up going elsewhere if you keep them hanging around for parts.

I'm not saying don't do it, but you do need to consider your costs (and implications) extremely carefully: it may appear at first glance that doing your own machining will save money - but if you lose customers through delays / damaged items etc, or you find times are tight because there's no work to put on the machine, it may well be that subbing it out is actually more cost-effective.

FWIW, the Proto Trak CNC systems may be useful to you - they are specifically designed for one-off / short runs and are easily and quickly programmed from job-to-job (look up South Western Industries, or XYZ Machine Tools in UK / Europe) if you do bring it in-house.

Hope that helps.

Adie you've made some very good points here, also by outsourcing the work i suppose you do pass on some of the liability as well.

Hi Prop man,

I've been down the same route - should I design and build a machine or buy one ready made and get producing quicker? I chose the 2nd route after 3 people said they would help make the parts for me then backed out. I can live without the hassle.

I chose Rhonmac in Wales after looking at many others. He seems to have been making and selling machines for a while and his large machines look solid although your requirements are pretty big. He's making me a small 460 x 600 x 100mm bench-top machine at the moment. While I'm waiting for it I can work on designs and all the thousand other things that will need doing.

Contact him (Google Rhonmac). Let me know how you get on.

Regards,

Keith.

One of the biggest mistakes I see when companies start looking for machinery is to look at the purchase price and not much further - only to find that costs spiral out of control. Indeed, it's not unknown for the final bill to be 3x (yes, THREE times) the original estimate in cases, due to poor cost anticipation.

It *should* go something like this:

Purchase price of machine.

Does the machine come with tooling / fixtures included? If not, what items do you need? How much does that cost? Do you need "sister" tooling (ie several cutters of same size / type to replace worn ones)?

Transport: is this being arranged by the machine supplier, and included in the price? Or do you need to arrange it yourself and pay it separately?

Workshop: do you have sufficient workshop space, or do you need to arrange one, or expand an existing building? What difference will it make to your rent and rates? If your altering an existing space, how much will alteration cost?

Installation: how do you plan to get it in the workshop? If its small, you may get it in with a forklift; if its a big machine, it may well need to be craned in through the roof - so you have the cost of removing and re-instating the roof section (how much?) plus crane hire. Crane hire itself could be £1500+ per DAY. If you have an existing factory / workshop, do you need to send non-essential staff home for safety or other reasons? How much is your likely downtime while your factory doesn't run (ie, how much production time is lost x number of staff) whilst you get the new machine in? Also with installation, your transport and crane hire (if it applies) and the roofing work (if it applies) need to be tightly co-ordinated: you don't want to pay an extra day's crane hire for example because something else isn't on site on time, or because your not quite organised with space.

Service supplies: electric / air / gas / water and any other supplies it may need: can you run it from an existing electrical system? Does the supply point need moved closer to the machines intended site? Do you need to run new cables? Indeed, is your existing power supply man enough for the addition of the machine anyway? If that machine has pneumatics (eg tool change carousels), have you got a compressor that can handle it? If not, that could become a second plant purchase in its own right, and needs to be costed in the same fashion. The same goes for gas / water / hydraulics if they apply.

Commisioning: Testing of the plant / system and making sure it functions as intended, and system hand over: is that included from the machine supplier, or is it charged separately?

Training: going back to my earlier point that the machine is worthless without a skilled operator, how much is training going to cost? Bearing in mind that some people learn skills more easily than others, how long is your anticipated training period? Or is it easier to employ someone who already knows what they're doing?

Finally, having gone through all that, how does the cost compare to sub-contracting the work? How much of a difference is there? How many items would you have to make (and sell) before you break even and start to show a profit? And how long (realistically) is it likely to take? Do you have / can you access (eg from your bank) sufficient funding to cover the bills for this period?

Hope that helps.

bloody hell !!! you guys make it sound like armagedon

when i started reading this thread i was thinking "yea man, pick yourself up a cheap cnc, throw it in the corner... press go and start printing money" :)

i somtimes think if we knew just how much blood n sweat was involved we would stay in bed and dream about how well it would have worked out if we had had the gumption.......

having said that it does sting when you bite off more than you can chew

Mark

Goes to show how blinkered you can get by pretty lights and all that glitters. I used to run my own business years ago and all i worried about was getting to work on time. judging business cost is a fine art and those that do it well succeed and those that don't get by or not at all. It's good to get a reminder sometimes and not just worry about 40% margins.......Times have changed?

ok ill take my blinkered optimism down to the shops and buy something shiny :wink:

LOL! shiiiiinnnyyy..........i like shiny....