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  1. #1

    CNCing Wet Wood

    Question for the group - I'm working on making some glass blowing molds (shown here a pint glass mold.) CNC cuts everything perfectly flat out of a block of maple. When I soak the wood in water so that it doesn't burn up I the wood warps which turns my perfectly round pint glass mold into an oval pint glass mold. Ive tried clamping the wood while it soaks to prevent the warping, that seems to help but doesn't prevent the problem. I am using oven dried wood and realize I should use green wood. Im curious if anyone has done any wood work on things that will be getting wet to see if there are other things worth trying? I have a surplus of dry maple hence the question as I would much prefer to use that than to buy new green maple. I know they make conditioner products to prevent freshly cut wood from cracking... has anyone used that for the opposite - to keep dry wood from warping when it gets wet again? Should I soak the wood and cut it on the CNC while wet? What would that do to feeds and speeds?

  2. #2
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    Re: CNCing Wet Wood

    Why is the wood charring to start with? Blunt tool, inappropriate speed / RPM / DOC? Wetting the wood sounds counterproductive to me.

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    Re: CNCing Wet Wood

    [QUOTE=CitizenOfDreams;2407818]Why is the wood charring to start with? Blunt tool, inappropriate speed / RPM / DOC? Wetting the wood sounds counterproductive to me.[/QUOTE}

    I'm guessing that it is the result of the contact with molten glass.I can offer very little advice on working with wet wood other than suggesting that you might try using quarter sawn blanks as they will be less liable to move.

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    Re: CNCing Wet Wood

    Oh, I see it now. I thought the wood was getting burned during the machining.

    In that case, how about soaking the wood and then drying it halfway? Dry enough to cut it, moist enough not to warp when wetted?

  5. #5
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    Re: CNCing Wet Wood

    Hi Egor - Have you tried plywood? maybe more stable. Peter

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    Re: CNCing Wet Wood

    Been in the woodworking trade for many years, but this is a new one for me. I live new Corning NY where Steuben Glass was. I remember watching those folks blowing glass and using wood forms to help shape the glass in process, but the contact was always little more then momentary. Also, the forms were of a general/generic shape, were always immersed in water and weren't intended as a clamped mold. I don't know if the forms were always in water, or were wetted just before use.

    Air dried quarter sawn wood might be a start (less likely to crack?), wetting only shortly in advance of applying the glass. But I think distortion of the wooden form should be expected. I would look to the glass container industry to see if there was applicable process info to be gleaned there.

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    Re: CNCing Wet Wood

    By the way; the conditioner for treating green wood that you spoke of is a glycol based product (I believe). The process uses the conditioner to displace the bound water in the wood (after soaking), thus stabilizing the material. Commonly used by turners to keep green wood from blowing up during rough shaping.

    That might offer an option, wetting the form just prior to use. Good luck with your project.

  8. #8
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    Re: CNCing Wet Wood

    Like Marv I've seen a lot of wooden forming tools used wet, but not closed molds like the ones you've made. Those are generally made from metal or graphite. Have you tried using aluminum instead of wood for this? Graphite is probably the best material to use, but aluminum is easier to deal with. If all you can use is wood on your CNC machine, you might try making a pattern in wood and taking it to a sand foundry for casting in bronze or iron.
    Andrew Werby
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  9. #9

    Re: CNCing Wet Wood

    Thanks for all the thoughts!

    Yes thankfully I'm not that bad at CNCing that the charing is from the tools. Pretty sure Biessa wouldn't have let me keep the machine!

    What you guys have likely seen while watching other people blow glass is referred to as blocks. They are used to shape and evenly cool the glass into a round shape for blowing it out evenly. These sit in buckets of water and only touch the glass for short bits of time and are dunked back in water when the glassblower starts to see the block drying out. This is a mould so it functions a little differently.

    Metal molds are possible but pose a whole different slew of problems - namely they need to be kept just the right temperature so as not to shock the glass when they are too cold or stick to the glass when they are too hot. They are used a lot in molds where the shape isn't radial and the glass won't be turned while in the mold and in high production facilities. Graphite is the most common and gets coated with a layer or cork that is sprayed with water. These last longer than wood molds.

    Because i'm not running a large number out of any of these molds wood would normally be the preferred method. And honestly I have a bunch of maple laying around so I've been trying to make it work. The answer may be it simply doesn't work.... Most of the high quality glass blowing things made from wood are made from cherry.

    Sounds like best options are:
    -Try the conditioner as why not and it may work
    -Try pre-wetting the wood before cutting it and let it dry a little
    -Try graphite

    Any Idea how a slightly wet wood affects feeds and speeds? Im assuming there is a higher likelihood of tear out? Obviously clean/dry all the tools after so I don't run into any rust issues.

    Any preferred sources for blocks of graphite? Any insight into CNCing graphite? I don't have a coolant system on my CNC will that be a problem?

    Thanks everyone!

  10. #10
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    Re: CNCing Wet Wood

    If you're cutting damp wood, yes to tear-out (likely). Make sure you use sharp, SHARP tooling. Probably HSS not carbide. True router bits, not end mills (geometry is different). Regarding graphite; how about a coating of graphite filled epoxy? Self lubricating during cutting, no need for coolant? No idea how it would react to heat.

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    Re: CNCing Wet Wood

    Without knowing the OP's location it isn't easy to recommend a source of graphite.I have seen graphite tooling used for composites and it does a good job at that sort of temperature (120 C) I am quite sure it will be very messy to machine and that the dust is a threat to anything electrical if it isn't totally extracted from the work area.It will also cost a lot more than wood.There is some information here: https://www.semcocarbon.com/blog/fiv...ining-graphite . I read an article in a UK woodworking magazine about 25 years ago on making a mould for custom wine glasses and my memory is telling me that it was not expected to have a long life.I can't remember what species was used.I would repeat my earlier suggestion that you should try to use quarter sawn sections of your wood to minimise movement.

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