mock up materials

[david lockwoodParticipant @davidlockwood10028]

Hi every one, I am starting to design a tool and cutter grinder for my workshop. I am making a mock up out of wood just to get my ideas straight. My question is, is there a material that I can machine / turn /thread etcetera, which would be cheaper than aluminium and preferably fast to machine? The wood I have is far too soft and comes off in chunks. I can get hold of some hard wood, yew and oak in small amounts but my expectation is that they will not take a thread. Any advice would be very much appreciated. >>

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Ps I know there are tool and cutter grinders in kit form already designed for me but I just fancy doing my own

[david lockwoodParticipant @davidlockwood10028]

which mateials are good to make a mock up

[MichaelRParticipant @michaelr]

I think engineering plastics would be your best bet, seehere

[macmarchParticipant @macmarch]

I cannot remember the name of it, but there is a material of a plastic nature that was used to prove the numbers when producing g code for cnc machines. It could even be screw threaded and tapped.

 

 

[Keith LongParticipant @keithlong89920]

Hi David

Just a thought for you, if you want fairly fine (6,8 10mm say) threads then using threaded bar (studding) cut to length would be quick and easy, and you can get “T” nuts from Screwfix or Toolstation that will go into wood with those threads and give you a metal insert. That way you can make just about everything in wood and still have operable threads. If you are thinking of large threads such as the coarse thread on the Quorn wheelhead support column they can still be cut in wood using virtually the same technique that Chaddock used, but instead of a milling spindle you’ll need to find a way of rigging a router to spin the cutter bit – the spindle speed for routing is about 10 times what you need for milling.

Keith

[david lockwoodParticipant @davidlockwood10028]

Thanks every one for the help. The T nuts sound like a good idea and I have also looked at the plastics web site which looks promising, the PVC looks like the best bet, also as it happens there location is less than 15 minutes from my house. College engineering sell test foam and I will ask them as to its suitability thanks again

David  

[JasonBModerator @jasonb]

Macmarch You are probably thinking of Trycut or similar, I did think of this when I saw the post but its not cheper than alloy. You can also make your own wax for testing machine setups but its not that strong.

 

http://www.collegeengineering.co.uk/Materials/introcnc.htm

 

I would glue up some MDF to get the thickness required and where it needs tapping just glue or screw in some inserts

 

http://www.isaaclord.co.uk/products.aspx?subCat=22&parentCat=1%2f22

 

Jason

 

[Gordon WParticipant @gordonw]

I’ve used flooring offcuts for this sort of thing, the better quality stuff is good and doesn’t warp. Also oak flooring offcuts. will take a coase tapped thread .

[Sam StonesParticipant @samstones42903]

Hi David,

I agree with STICK and JasonB wrt plastics materials for prototyping.

RPVC (rigid poly vinyl chloride) has several attributes. It’s nice and rigid, there’s no grain yo worry about as in wood, and it glues a real treat. The stuff sold at plumbing outfits for joining RPVC pipes is preferable.

Machining is easy, although when turning, static charges will begin to attract the swarf. This stuff will readily wrap itself around the workpiece requiring frequent intervention. While it’s not good practice, I try to grab the free end and drag the swarf away from the workpiece as a single thread, but be careful, especially near the chuck jaws. A vacuum cleaner can be used to aspirate the swarf in a similar way.

Unlike certain of the softer plastics, RPVC does not exhibit the tendency to warp as you machine it (a bit like the stress-relieving effect with bright drawn mild steel). Some of the polyolefins like high density polyethylene and polypropylene in sheet form will twist and distort when the surface `skin’ is disturbed.

Like most thermoplastics, RPVC has a low thermal conductivity AND a low softening point, and will easily melt if there is too much frictional heat being generated. For example, when tapping holes, try to avoid running the tap in and out too quickly, otherwise you may lose the thread. Slightly softened water as a coolant works well to reduce the temperature of the section being cut. A bit of spit on the tap works if you’ve nothing else to hand.

I like polyacetal too, but gluing doesn’t work with normal adhesives. I’m not sure if there’s a surface primer which works. Also, be aware that should any of this material be burnt, the fumes are extremely noxious.

In the plastics industry, a simple bench test for determining the type of plastic is to burn a small sample and smell the fumes.

DO NOT DO THIS WITH POLYACETAL.

Have fun, and feel free to drop me a line, if you think I can help.

Sam

[VersabossParticipant @versaboss]

Sam Stones wrote:

>In the plastics industry, a simple bench test for determining the type of plastic is to burn a small sample and smell the fumes.

DO NOT DO THIS WITH POLYACETAL. <

Why? Polyacetal consists of carbon, hydrogene and oxygene. Certainly not more harmful than a wax candle.

See http://de.wikipedia.org/wiki/Polyoxymethylen

in German, sorry

Greetings, Hnasrudolf

[Sam StonesParticipant @samstones42903]

Versaboss wrote :-

“Why? Polyacetal consists of carbon, hydrogene and oxygene. Certainly not more harmful than a wax candle.”

This is quite a digression from David Lockwood’s request for mock up materials, but here goes :-

I’m not a chemist although I started in the plastics industry in 1950. I’m not medically qualified either. However, I have to say that on their own under normal conditions, the atoms Versaboss mentions are not particularly harmful.

Like most molecules however, it’s how the atoms are arranged in combination which determines their properties. Please don’t be offended, but that’s basic (polymer) science. As an example, watch what happens to another `simple’ molecule – nylon (polyamide) in a microwave oven. (Put a receptacle under it, otherwise you might need a new oven.) Polyamide contains hydroxyl groups (hydrogen and oxygen again) which are directly involved in the heating process.

Meanwhile, might I suggest that if you want to try the simple bench test on polyactal, go ahead and take a good sniff.

YOU HAVE BEEN WARNED (again)

I would suggest however, that you will never forget the experience.

Those who know about this test will, as a precautionary measure, wave the fumes towards their nose in order to avoid getting a hooter full. Be aware that burning drips of polymer, can result, so there’s another warning.

In closing, and with respect, I would not be comparing polyacetal with candle wax at any level.

Best regards,

Sam

[Billy MillsParticipant @billymills]

Sam

Perhaps you have made an error in recommending the plastic burn test on this forum which is open to all. If you are not experienced in the test then you will not understand the smell and it’s implications. If you know about the method then you don’t need to be told about it.

 

There are many common materials such as PVC and PTFE that should NEVER be burnt by untrained people. Both plastics produce deadly gasses. Simplistic chemistry  is very dangerous,  Carbon and Nitrogen are  common elements in plastics , one compound produced by burning is cyanide. Chlorine containing plastics like PVC will produce HCl which will -when breathed in- produce hydrochloric acid inside your lungs.There are many other very dangerous compounds formed by low temp burning in air.

 

I would advise that -unless you really have the experience to understand sample burning- you NEV ER attempt this very dangerous process but get your materials from reliable sources.

 

Back  to the thread, hardwoods do thread but the grain limits the load. The real question is what do you want to do with the model? If it is a visual mock up then foamed polystyrene plastered and sanded is dirt cheap  and will allow clearances and form to be seen.

 

 Foam board and card are also easy, cheap and quick for a non working model.

 

Unless plastic or ali is scrap it might cost as much as the finished model but it would be approaching the stiffness of the final product , is that what you want?

 

 

regards,

Alan.

[david lockwoodParticipant @davidlockwood10028]

Thanks again for all the interest

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Alan what I am probably best looking for at this stage is what ever is cheapest. I can then make as many mistakes as it will take (probably a lot) and not worry about the price of remaking the part. Polystyrene may be good for some parts just to show the space they will take up if nothing else. The mock up I am working on at the moment is most like an ideas board that I will probably change several times before I am finished it will not need to be anything like as rigid as the real thing but I would like the moving parts to actually move and be as real as possible when it is finished.

 

 Looking at the price of PVC compared to aluminium I would say it shows a considerable saving, on the web site shown by stick there is PVC and acetal  are these the same as or close enough to polyacetal and RPVC as mentioned by Sam Stones?

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David

[Billy MillsParticipant @billymills]

David,

Why not use MDF? it is readily available in sheet from 3mm up, easy to cut and glue into any size block you want. You can saw, turn, bandsaw, drill, tap,mill and sand the stuff. If a bit does not work make another for pennies.  You can also shape it by sanding or carving when the model is assembled. But do wear a dust mask.

 

I have used lots of the stuff over the years for all sorts of lash-ups and jigs. It is often a good stand in for test foam for CNC checks and is free of the grain issues with real wood or ply and tends to be quite stable. It is very useful for vac form moulds too.

 

Regards,

Alan

 

 

[Sam StonesParticipant @samstones42903]

To everyone reading this thread, I agree entirely with Alan Gray 1, when he suggests that I made an error in introducing the bench test. In advising Versaboss of the dangers associated with polyacetal, I made too strong a point.

Although the technique is well documented in several raw material suppliers publications, including the multi-national company I worked 24 years with, I should NOT have gone so far into this subject.

My apologies, and be VERY CAREFUL.

 

Sam Stones

[TerrydParticipant @terryd72465]

I agree with Alan and Keith above, use mdf, laminated if necessary, and for screw threads use studding (cheap as chips) and T nuts (or even standard nuts epoxied into place).  I don’t think that you need to buy esoteric materials for a simple mock up. Then you won’t need to do flame tests .

 

Terry

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