Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
-----
VDI What does this mean in surface finish terms?
Q. Is there anyone with knowledge about which surface VDI No. to use when designing light pipes.
Best regards,
J
- Stockholm
May 12, 2022
⇩ Related postings, oldest first ⇩
Q. Our company is a supplier to the automotive industry worldwide. We are a plastic injection moulding company in the North East of the UK and manufacture our own mould tools. For surface finishes on our tooling we have used VDI comparator blocks. Can anybody tell me what the initials "VDI" stand for?
Cheers.
Plastic Injection Molding & Tools - Stockton on Tees, Cleveland, UK
2004
Q. I also want to know about the VDI finish and its conversion in Ra value. Is it EDM related term if yes then how is it controlled?
Waiting for your positive response,
designing - Udaipur, Rajasthan, India
2004
Ed. note: Since 1989 this forum has enjoyed the camaraderie & warm aloha which real names & locations afford. If you're not into that spirit, those who do post with their real name may be less likely to engage with you.
Q. Same questions as previously posted by others: a formal comparison of VDI to Ra? information on VDI - what is it?
Ray Smith- Huntingdon, UK
2004
A. Hi. VDI = Verein Deutscher Ingenieure, the Society of German Engineers. There is a VDI scale for surface finishes, which is widely but not exclusively used in the EDM field. My lack of German has hampered my search for a cross reference chart or a description of what the VDI scale is about, but hopefully a reader will help.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. I had the same problem with VDI grades. The solution came from Rubert & co. England. They offer EDM finish scale to VDI 3400 standard. It comes with comparison table Ra values. For more information: www.rubert.co.uk/comparison.php ⇩
Medical equipment - Helsinki, Finland
2004
Ed. update: The above link is broken. Thankfully, the Internet Archive saved a copy here 
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A. I have the same problem to find a correspondence between VDI and Ra, and after some search I made this comparison table :
VDI RA (in micrometer) 10 0.32 12 0.4 15 0.56 18 0.8 21 1.12 22 1.26 24 1.6 27 2.24 30 3.15 33 4.5 36 6.3 39 9 42 12.5 45 18
Best Regards.
David Bourdin- Bobigny, France
2005
Q. We have the VDI 3400.39 grain call out on a print for a part we are to supply. Can anyone tell me the depth of this grain and the draft required to eject the part with this grain?
Sabrina Arsenault- Barrie, Ontario, Canada
2005
A. Bayer Plastics has some good Information about surfaces and injection molding available on their web- Site.
According to a (German) Document the VDI surfaces correspond to the following Ra / Rz Values and require the following drafting angles:
VDI; Ra; Rz; DA-PA; DA-PC; DA-ABS 12; 0,40; 1,5; 0; 1,0; 0,5 15; 0,56; 2,4; 0,5; 1,0; 0,5 18; 0,80; 3,3; 0,5; 1,0; 0,5 21; 1,12; 4,7; 0,5; 1,0; 0,5 24; 1,60; 6,5; 0,5; 1,5; 1,0 27; 2,24; 10,5; 1,0; 2,0; 1,5 30; 3,15; 12,5; 1,5; 2,0; 2,0 33; 4,50; 17,5; 2,0; 3,0; 2,5 36; 6,30; 24,0; 2,5; 4,0; 3,0 39; 9,00; 34,0; 3,0; 5,0; 4,0 42; 12,50; 48,0; 4,0; 6,0; 5,0 45; 18,00; 69,0; 5,0; 7,0
DA-PA = Drafting Angle for Polyamide
DA-PC = Drafting Angle for Polycarbonate
DA-ABS = Drafting Angle for Acrilnitrile-Butadiene-Styrol
glass reinforced materials require more drafting
- Langendorf, Switzerland
2006
But be careful: The table with the VDI related draft angles Mr. Lorenz Wiedemar provided (he says it's from BAYER plastics) is possibly not right!
For example:
STANDEX International communicates that their VDI 36 equivalent (MT 11540) requires minimum 3,5 even for PA !!
So just ask your surface supplier BEFORE being fooled by this table (like me).
- Fuerth, Bavaria, Germany
February 22, 2012
Hi, Simon. Thanks!
I've never found any surface standards for which "conversion" or "substitution" is actually possible. Rather, it's like comparing people's height vs. weight, or an engines torque vs. horsepower -- one parameter tends to "track" the other, but they cannot actually be converted. We see this in Ra vs Rz where the "conversion factor" must be low in one direction to be relatively safe and much higher in the other direction to be relatively safe because they are simply not measuring the same thing.
My unfortunate lack of German prevents me from understanding VDI standards and how they translate to other systems, but it would greatly surprise me if there is an actual "conversion"; I'll bet it's "usually roughly equivalent to somewhere around . . ." :-)
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. VDI = 20log(10Ra)
James Lai- JB, Malaysia
2006
A. Nr is the number of roughness or the class, using VDI d
Nr=20*log(10*Ra)
Try with the equivalence table.
- Basq Country (north of Spain)
April 4, 2011
A. VDI Table
In the following, you can determine the roughness for your application according to VDI table.
VDI3400 Ra = AA = CLA ISO1302 Rt 0-45 µm µinch N3-N10 µm ----- ----- ----- ----- ----- 0 | 0.1 | 4 | N3 | 1 | 0.11 | 4.4 | | 2 | 0.12 | 4.8 | | 3 | 0.14 | 5.6 | | 4 | 0.16 | 6.4 | | 5 | 0.18 | 7.2 | N4 | 6 | 0.2 | 8 | | 7 | 0.22 | 8.8 | | 8 | 0.25 | 10 | | 9 | 0.28 | 11.2 | | 10 | 0.32 | 12.8 | | 11 | 0.35 | 14 | N5 | 12 | 0.4 | 16 | | 1.6 13 | 0.45 | 18 | | 14 | 0.5 | 20 | | 15 | 0.56 | 22.4 | | 3.2 16 | 0.63 | 25.2 | | 17 | 0.7 | 28 | | 18 | 0.8 | 32 | N6 | 5 19 | 0.9 | 36 | | 20 | 1 | 40 | | 21 | 1.12 | 44.8 | | 7.5 22 | 1.26 | 50.4 | | 23 | 1.4 | 56 | | 24 | 1.62 | 63 | | 12 25 | 1.8 | 72 | N7 | 26 | 2 | 80 | | 27 | 2.2 | 88 | | 16 28 | 2.5 | 100 | | 29 | 2.8 | 112 | | 30 | 3.2 | 125 | N8 | 20 31 | 3.5 | 140 | | 32 | 4 | 160 | | 33 | 4.5 | 180 | | 25 34 | 5 | 200 | | 35 | 5.6 | 224 | | 36 | 6.3 | 250 | N9 | 37 37 | 7 | 280 | | 38 | 8 | 320 | | 39 | 9 | 360 | | 46 40 | 10 | 100 | | 41 | 11.2 | 448 | | 42 | 12.6 | 500 | N10 | 60 43 | 14 | 560 | | 44 | 16 | 640 | | 45 | 18 | 760 | | 85Qijin Wu
- Nanjing Jiansu Province, P.R.China
2007
Q. Besides surface finishing of VDI standards, there is another standard SPL-2, would like to know the relation of VDI versus SPL-2, how to convert SPL-2 into VDI?
Cherwei Li- Penang
August 16, 2008
Q. Hello, is there anybody who knows how is possible to compare VDI scale to SPI scale?
Paolo AprileDatasensor - Bologna, Italy
October 27, 2008
Q. Hi, can anyone help me with VDI 27 (RA 2.24) finish? I need to know if it's like mirror polished or just EDM textured finish.
I am trying to order plastic molds and need Mirror finish polish for better clarity of molded parts, my mold maker says that VDI 27 is just EDM textured finish.
Any documented help on this will be highly appreciated.
- Dubai UAE
April 29, 2013
A. VDI is a textured finish usually from spark eroding, for polished finish you should work in microns, lower the number higher the polish.
Daniel Wood- Blyth England
June 4, 2013
Q. Hello,
We are a Rubber parts manufacturing company, one of our German customers has sent us a drawing where on one surface they have marked "surface erodes - VDI Cl.27". I wanted to understand whether this mean that the surface should be rougher than VDI Cl.27 or smoother. Our normal surface is polished, would that be accepted in this case or not? Thank you.
Regards,
Darshan
rubber industries - Mumbai, India
August 27, 2014
A. VDI, while I am less aware of the call-out, is an EDM finish loosely related to the roughness of the resultant finish. SPE/SPI is a modified surface finish ranging from D-3 to A-1. D surfaces are media blasted. C surfaces are stone polished, B surfaces are paper abraded. A surfaces are diamond polished.
http://sftusa.com/polishing/spi-guidelines-chart.html ⇩
This page has the complete definitions for SPI finishes.
- Crawfordsville, Indiana, USA
November 6, 2014
Ed. update 1/20/24: That site is not loading. Thankfully, Internet Archive saved a copy of the chart
These days information often appears on the internet, then disappears forever. If that is a concern to you please consider a donation to The Internet Archive.
A. See chart I obtained, with SPI, VDI and Ra Rz, in my flicker:
https://flic.kr/p/rnv6qr
Medical Devices - Swansea, Wales
February 26, 2015
Ed. update 1/20/24: Andrew's chart is still there.
A.
VDI=20*LOG(10*Ra)
Ra=10^((VDI-20)/20)
Rmax=4*Ra
DISEñADOR DE MOLDES - BUCARAMANGA, SANTANDER , COLOMBIA
February 6, 2018
A. Check out Xometry - Injection Moulding Surface Finishes : SPI and VDI
Gives handy SPI and VDI conversion charts.
Process engineer - Skipton, North Yorkshire, UK
November 24, 2021
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