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Forum topic by Spence0123 posted 04-18-2020 12:51 AM 586 views 0 times favorited 12 replies Add to Favorites Watch
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Spence0123

2 posts in 80 days


04-18-2020 12:51 AM

I am in the process of making a sign for events going on in the world. It has the words “2020 strong” pocketed around a circular border. I am having a few issues though, the first being the burrs left behind and the second being. Some letters are broken off. Any advice.
Tool used: .0625in 2 flute endmill at roughly .042in depth per pass. Total depth is .125in


12 replies so far

View JohnMcClure's profile

JohnMcClure

1017 posts in 1412 days


#1 posted 04-18-2020 01:04 AM

MDF doesn’t handle these fine cuts well. You need a more solid material. Walnut and maple do really well with this, but are extremely expensive by comparison. I have 3 recommendations:
1. Use a Vbit and “prism carve” the letters. I use 60 degree from mcmaster. The relief angle makes your letters much stronger. Save time by doing clearance with the end mill before using the v-bit.
Or
2. Pocket the letters instead of the area around the letters.
And or
3. Not sure if it would work, but seal the MDF with shellac (Zinsser SealCoat or similar, cheap at Home Depot). I’m thinking this will make the surface stronger, leading to less burrs and possibly less breakage.

-- I'd rather be a hammer than a nail

View John Smith's profile

John Smith

2429 posts in 935 days


#2 posted 04-18-2020 02:31 AM

Spence – how big will your sign be ?
how many will you make ?
for inside or outside use ?
how long do you want the sign to last ?
can you post a sketch of your project ?
loose filled material like MDF will never give you good results.
depending on the answers to the above questions would determine
what material would be the most appropriate for your project.

.

-- there is no educational alternative to having a front row seat in the School of Hard Knocks. --

View Tony_S's profile

Tony_S

1329 posts in 3855 days


#3 posted 04-18-2020 10:10 AM

That doesn’t even look like MDF. It looks more like hardboard?
I’m far from an expert on MDF, but I’ve never seen it with fibers that course, or ‘hairy’. Hardboard does get hairy though unless it’s tempered hardboard.

What little experience I have with this type of cnc work(sign making with mdf) went fine. I can’t give you spindle speeds or feed rates, as I’m not an operator, but If I remember correctly, the tooling was nothing more than a combination of solid carbide v groove’s and 1/8” down shear’s.

That’s a lot of miles to put on a 1/16” bit….are you keeping your tooling sharp? Any type of fiber board is murder on cutting edges. Even carbide.

-- “Wise men speak because they have something to say; fools because they have to say something.” – Plato

View DS's profile (online now)

DS

3503 posts in 3192 days


#4 posted 04-18-2020 11:17 AM

Fuzzy cuts usually means it’s a dull tool.

I wouldn’t be doing this entire sign with an 0.0625 bit.
MDF is hard on router bits and that is a big ask of such a small bit.

First, I would use a v-bit to outline the letters, then find the largest bit that fits the in-between spaces and remove the bulk of the material, then step down in diameter to remove the left-over corners.

Sure, it takes a bit more effort to program than a simple raster scan with a tiny bit, but the results will be much faster, and much cleaner.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View tvrgeek's profile

tvrgeek

988 posts in 2421 days


#5 posted 04-18-2020 12:43 PM

Have you considered soaking it in some penetrating sealer to give it more strength?

View John Smith's profile

John Smith

2429 posts in 935 days


#6 posted 04-18-2020 01:45 PM

I think that most experienced CNC operators would STOP operations
at the very first sign of trouble – there was no reason to continue this
project after the first few inches were seen as a disaster.
when the O/P returns with answers to his project, better options of
what material to use can be offered.

.

-- there is no educational alternative to having a front row seat in the School of Hard Knocks. --

View Nubsnstubs's profile

Nubsnstubs

1723 posts in 2502 days


#7 posted 04-18-2020 01:50 PM

If you were using the MDF that is the heavier denser stuff, you might have better luck. The new lightweight MDF will leave the fuzz…......Jerry (in Tucson)

-- Jerry (in Tucson) www.woodturnerstools.com

View Spence0123's profile

Spence0123

2 posts in 80 days


#8 posted 04-19-2020 02:31 AM

A little background on me. My specialties is working with alum/steel and some acrylic. I have very little experience in wood working. My boss told me that it was MDF and so I went about doing the project. We have talked about using acrylic for it and I don’t have the design with me and won’t have it until Monday morning until I go back in. We wanted to use a cheaper material so I’m not sure acrylic would be the only one we would make it out of. Any woods you guys would recommend outside of MDF (obviously) and on the cheaper side.

View John Smith's profile

John Smith

2429 posts in 935 days


#9 posted 04-19-2020 12:05 PM

Spence, reach out to my friend and colleague David Falkner
on his MDF CNC projects. he just finished this piece. he can share some
of his notes with you on the MDF issues you are having.
(he is also a member on this forum, just not as active as I am).
you can see how much detail he put into this design using 1/2” MDF.
what is the size of your project piece ??

.

-- there is no educational alternative to having a front row seat in the School of Hard Knocks. --

View gwilki's profile

gwilki

352 posts in 2246 days


#10 posted 04-19-2020 01:43 PM

I do quite a bit of CNC routing in MDF and I can get very clean cuts. As Tony_S said, that does not look like any MDF I’ve used. With sharp mill and the right feeds and speeds, you should be able to get clean, sharp cuts. The letters will not be strong and will break off easily, but as there will be no forces on them, that should not pose a problem.

I would reduce your pass depth to no more than half the diameter of the bit, keep your plunge rate low, run at least 12000 rpm and use a new downcut mill. MDF will dull a bit in no time.

What software are you using?

-- Grant Wilkinson, Ottawa ON

View Underdog's profile

Underdog

1508 posts in 2808 days


#11 posted 04-19-2020 03:22 PM

You’re using a lower quality MDF. You need to buy a door grade MDF in order for it to machine well. It will have more glue content. I could get some very nice cuts in that stuff. I made raised panel doors that after painting you could hardly tell the difference between it and a five piece wood door. You will have to sand and prime no matter what grade of MDF though. But a door grade MDF will not be nearly as bad as what you’re showing us.

Some of your modeling might be part of the problem. You need a good amount of draft for lettering – also make them low profile. As you have found the MDF does tend to shear off.

As said above, you do need sharp tooling.

-- Jim, Georgia, USA

View Ger21's profile

Ger21

1099 posts in 3903 days


#12 posted 04-19-2020 03:27 PM

What you want is called “super refined” MDF. Tends to be much lighter in color, and more uniform density.
You also want to use downcut bits.

-- Gerry, http://www.thecncwoodworker.com/index.html http://www.jointcam.com

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