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Dave Sheldrake
09-03-2013, 6:11 PM
While I have a pretty reasonable knowledge of lasers I know nothing about wood (other than it comes from tree's) I've been asked about relative humidity storage for woods and plys for use on a laser and if there is a "recommended" RH value they should be stored at?
Would "cooking" wood materials make for better cutting? (I did cook some ply "Baltic Birch" that cut very quickly but have no idea if I damaged it's structure) does low RH material cut better?

Any thoughts or experiences welcome :)

thanks

Dave

Chuck Stone
09-03-2013, 7:46 PM
I don't know about 'cooking' but I'm pretty sure the moisture content
would change with the weather pretty quickly. (much to the chagrin of
any pen turner who has tried using snakewood, ebony and such)

If you try to store under certain conditions (say.. maintaining a certain RH
or temperature) you're certainly looking at some sort of powered unit,
so that would have to figure into your cost of goods, too.

Alexa Ristow
09-04-2013, 6:20 AM
We have plenty of experience with the effect of RH on MDF cutting. While I cannot quote actual RH values, we do know that on humid days, we can lose up to 20% of speed on 3mm MDF.
We will sometimes keep a few boards inside the less humid house and only take them into the Workshop prior to cutting.

Regards,

Alexa.

Mike Null
09-04-2013, 6:56 AM
Dave

Humidity will definitely have an effect on cutting wood. The guys over in the woodworking forums are experts and can give you some info.

As for me, I make sure any wood I engrave is either air dried or kiln dried before engraving. I store all my wood in my air conditioned basement where I also have a dehumidifier if I need it.

If you engrave green wood you can be sure it's going to check, warp or twist not long after you use it.

I just engraved a cross section of a tree---still green---and I warned the customer that the checking would only get larger. The wood had special significance for the customer.

There are meters you can buy online or at woodworking stores to measure wood humidity. If you are storing a lot of wood there are ways to store it which you can see by doing a Google search.

Bottom line--high humidity ain't good.

Dave Sheldrake
09-04-2013, 6:58 AM
Thanks Chuck, Alexa, Mike

MDF does tend to be a bit of a sponge, looks like I'm going to be going temp control in the wood store. I keep upwards of 1,000 full sheets in at any given time so anything that gives more reliability is going to be an improvement.

cheers

Dave

Dan Hintz
09-04-2013, 8:18 AM
Ideally, you want to be in the high single digits... local atmospheric conditions can change this, obviously. The more water content you have in the wood, the more power you need to get through, but in the end you want the wood to be similar to local conditions to cut down on warping and checking.

Dave Sheldrake
09-04-2013, 9:57 AM
Thanks Dan,

I'm going to see if I can get different RH value woods and try them out :)

cheers

Dave

Mike Null
09-04-2013, 10:26 AM
Finishes (shellac, varnish, paint, lacquer) protect wood against absorbing humidity but not totally.

Dave Sheldrake
09-04-2013, 11:29 AM
Just ordered a meter for wood to measure moisture content. Once I have some results I'll post them back :)

thanks

Dave

Dan Hintz
09-04-2013, 12:29 PM
Since you're working with ply rather than solid wood, I'd suggest a pinless meter.

Dave Sheldrake
09-04-2013, 1:12 PM
Thanks Dan :)

added a pinless to my order :)

cheers

Dave

Johan de Waal
12-13-2013, 11:31 PM
Hi Dave,

Any feedback on this topic? Here in SA we are entering our rainy season ( my first one with the laser) and it seems i can't run my laser at the speeds and power settings i used to run on 3mm mdf that I used a more month ago. Checked all the basics like alignment, cleaning etc. Only thing that has changed is the weather -more hot and humid and was wondering if this could be the source of my frustration?

Thnx

Martin James
12-14-2013, 10:12 AM
Dave a 4 pin meter is only 10-20 you can test it on your palm to see if it is calibrated, should always read the same. While on meters I also recomend a IR thermometer. about 50, get the smaller spot size. Then for example you can read the temp on various objects like motors bearings to see what is heating from friction.

cheers m

John Pletcher
12-14-2013, 11:20 AM
To maintain a moisture content of 6% to 8% typical of wood for use in interior applications, the relative humidity should be maintained between 35% and 45%. An excellent reference text to have on hand is "Understanding Wood, A Craftsman's Guide to Wood Technology", by Bruce Hoadley. My copy is well used.

John

Dave Sheldrake
12-14-2013, 4:05 PM
Been playing around with primarily MDF to see what differences in RH make. HUGE HUGE variation in cut-a-bility as soon as RH increases.

Even leaving a sheet in the lasers overnight with the usual drop in night time temperatures makes a big difference.
I'm now keeping the unit heaters on the same temperature settings at night as I have them on during the day. It adds to my unit heating costs buts has reduced loss of throughput for failed cuts by 20%

cheers

Dave

David Somers
12-14-2013, 4:17 PM
Dave,

If you have a de-humidifier you might try that instead of the heater and see if that gives you as good a result, and perhaps takes less to operate than a heater?

Dave

Dave Sheldrake
12-14-2013, 7:33 PM
Thanks Dave, I'll have a look at trying that, it's a pretty big area so I'd probably need a few of them, MDF is the one that causes me the biggest problems (and the most backache after 4,500kg turned up late yesterday and I had to move it).

It has to be stored flat on railed shelves so loading each sector with sheet takes some time :) best fun is yet to come running it all through a wall saw to get the sheet sizes I need!

cheers

Dave

David Somers
12-14-2013, 7:55 PM
Dave,


Ick! That doesn't sound like fun. Be careful. Had back issues years ago and it was misery until I finally got it squared away. I am very cautious now.

Are you familiar with this method of carrying sheet stock with a rope?

277128
I would be happy to swing by and help you move it next time....but I have a feeling that might not work well ! <grin>

Dave

Dave Sheldrake
12-14-2013, 10:30 PM
After the 6,000 mile swim my friend I think you'd be in the same state as me ;)

A lot of it is Finsa 2mm stuff with Medite Premier in 3.2 / 4.2 / 6.4 and 9.2mm so a bit flexible :(

cheers

Dave

Chuck Stone
12-15-2013, 12:13 AM
A lot of it is Finsa 2mm stuff with Medite Premier in 3.2 / 4.2 / 6.4 and 9.2mm so a bit flexible :(


Ah .. see, you don't need the wall saw after all.
It's self cutting!

Dave Sheldrake
12-15-2013, 6:24 AM
I have a big table saw Chuck but after asking around about using it on full sheets a few wood people (I know nothing about woodworking) suggested I should be very careful using a table saw (without a sliding gizmo) on it for full sheets so went and got one of these,

http://www.axminster.co.uk/safety-speed-cut-c4-panel-saw

It seemed like a good idea at the time anyways :)

cheers

Dave

Dan Hintz
12-15-2013, 7:54 AM
If you're cutting a lot of sheets goods, that's a good investment. Less time moving stuff on/off a horizontal table, less back-breaking work, etc.

Martin James
12-16-2013, 1:58 PM
dave if you had 1000 bottles of port, then you would have the cellar. Now days wine cellars are "installed" vapor sealed, humidity controlled rooms.

wood workers use a similar idea to slow the drying process to prevent warpage.

A good place to use up all your warped sheets of MDF.

frame, mdf, plastic sheeting, fan, dehumidifier, door, vent, light

thin strips between mdf sheets, weight on top

don't forget to read up on how temperature effects humidity.

cheers M

Dave Sheldrake
12-16-2013, 2:06 PM
Thanks Martin, I'm looking at dedicated storage now having seen how much RH affects cutting quality, I made the mistake a few years back of storing a load of sheets on their edge....ended up throwing the whole lot away.

The saw is a good one Dan, not really a professional piece of kit but so much easier than swinging sheets around, it made installing in the unit a bit easier too, one of the machines the factory inspector always made a line straight for was the table saw so having something with no exposed blade should keep the HSE happy :)

It's sings a bit from the tube resonance but it's easy to use for somebody like me that knows very very little about woodworking. I've never liked table saws or horizontal mills and avoided them where possible but using a circular hand held is just too much work for me if the guys are busy and I end up cutting sheet.

cheers

Dave