What to do when an etch drawing is bounced by PPD?

Dog Star

Western Thunderer
We have submitted out first QCAD produced drawing to PPD... and PPD has advised that details on our drawing are outside of the recommended limits. PPD has suggested that the smallest holes in our drawing are not guaranteed to etch through... rather the "etch through" holes could become "dimples" on either side of the material.

Our drawing is for brake parts which are suitable for a 7mm scale version of a 9'0"wooden underframe with 12" solebar, the drawing is produced from the appropriate drawings of the RCH 1907 specification for 8T and 10T mineral wagons. We have used the PPD guidelines for etching tolerances and recognise that some aspects of our work does not conform to those guidelines, specifically the diameter of holes for "pins / bolts", for example to pins/bolts at either end of the brake push rods and it is just these holes which are the subject of PPD's concern.

We have asked for 0.45mm Nickel Silver... PPD says that changing to 0.3mm reduces the recommended tolerances such that our drawing is acceptable. We do not want to go to 0.3mm as we feel that 0.3mm is not thick enough for all of the parts in the drawing, for example:- V hangers, brake levers and brake lever guards. Separating the parts into two sheets, one at 0.3mm and one at 0.45mm makes the project non-viable on a cost basis.

Seems to me that there are three options:-

1/ use a different photoetch company which works to more relaxed standards;
2/ accept PPD's warning and go-ahead, see note below;
3/ enlarge the holes and risk break out to edge of the part, (think adjustment holes at one end of a brake push rod).

What does the WT-experience suggest is the way forward?

Note:- many of the parts on the Exactoscale brake gear etch require holes to be drilled to size, Exactoscale used 0.5mm N/S and some holes are circa 0.4mm diameter after etching. I am lead to believe that Exactoscale may have used PEC in Walsall for their etch products.

thank you and regards, Graham
 
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Mike Garwood

Western Thunderer
I've had discussions with PPD over tolerances in etching. It's usually boiled down to, we shall etch it... but they advise that you're pushing the tooling to it's limit and it may not etch correctly or rather it may not come out as designed.
I've always taken the chance and asked them to proceed. The results have been mixed, some have etched as I intended, others have been over etched. But most have been usable. I etch for my own use, not for a commercial purpose.
Usually, it's down to you as a client to tell them what to do, the consequences and outcome are yours to bear after their advice.

Good luck

Mike
 

richard carr

Western Thunderer
Graham

Just go with it, if you get dimples you will need to drill them out but at least you will know where to drill.

They are over cautious if you ask me.

Richard
 

simond

Western Thunderer
I have used PPD for work, we have had discussions regarding some of the limits of my designs, I incorporated some but not all of their suggestions, and the results have been entirely satisfactory, and have also been repeatable.

I’d echo Richard’s comment regarding having dimples to drill as even if they do etch through, they’ll probably be under size due to the cusp, so you’re likely to have to drill through anyway.

I think I’d go for it.

fingers crossed
Simon
 

LarryG

Western Thunderer
Same here. Holes that are too small are easily drilled out, in fact this is sometimes preferable. I have asked an etcher to go ahead on some projects in the past because I was deliberately experimenting with ideas to to find out what was possible. Over-etching is the biggy. I threw several sheets away once when parts were falling apart at fold lines due to over-etching.
 

JimG

Western Thunderer
I had a similar thing with my first etch at PPD. It was for an S scale sprung "W" iron using .375mm nickel silver and I was particularly concerned about getting the slot for the 2mm axle bearing "Goldilocks" correct - not too tight and not too loose. there were also 0.4mm holes for the spring wire. The first photo tool worked very well with the bearing slots just right and the 0.4mm holes were dimples. The next attempt with some adjustments was nowhere so good with the bearing slot being too wide. When I talked to PPD about it, they said that the operator had over-cooked the etch to get the 0.4mm holes etched through which had affected everything else. They very kindly re-did the etch for free with no over-cooking and all was well. Ever since I always state with an order for this etch that the holes should be left as dimples.

This was several years ago and I can't remember there being any warnings on PPD's web site at the time. I suspect that they have brought in their minimum specs to avoid problems.

I also did another etch a couple of years ago using tab and slot and the same happened with the slots - first photo tool worked, but with the second photo tool, the slots were too tight. We had another discussion and I agreed to open up the slots even though I had been using the accepted calculation for setting slot widths. I suspect PPD want us to err on the wide side to give them some leeway on the etch duration.

Jim.
 

adrian

Flying Squad
Graham
Just go with it, if you get dimples you will need to drill them out but at least you will know where to drill.
They are over cautious if you ask me.
Richard
Agreed - although for holes that small I would always prefer to drill them out anyway. As an alternative why not leave them as half etched dimple on one side only. Just use them as location marks for drilling out to size.
 

simond

Western Thunderer
An under etched hole is not an issue if it can be drilled. An under etched slot in a fragile part is another story.

it should be possible to put some sacrificial test slots on the sheet, and ask them to take it out when the light shines through. Whether this is acceptable to PPD or any other etcher, I don’t know.

Atb
Simon
 

Eastsidepilot

Western Thunderer
To be honest from a builders point of view I'd much rather have a dimple mark to drill than a hole already in place, as then I can make the hole dia. the size I want it to be.

Col.
P.S. There's probably an old joke in that somewhere :D
 

Dog Star

Western Thunderer
Thank you to all who have contributed to this topic. We have asked PPD to go forward with pur drawings as is and to not over-etch to achieve those holes which are outside of the recommended tolerances.

regards, Graham
 

BrushType4

Western Thunderer
Thank you to all who have contributed to this topic. We have asked PPD to go forward with pur drawings as is and to not over-etch to achieve those holes which are outside of the recommended tolerances.

regards, Graham
Good luck and I think you’ll be addicted now you’ve gone down this path. :)
 

Dog Star

Western Thunderer
... you will be addicted now you’ve gone down this path. :)
Truly and I shall continue to take the medicine.

I blame Chris (@ChrisBr) for the potential addiction, what with him encouraging us to learn QCAD and his willingness to drink tea a change in approach to modelling wagonry was inevitable.
 

mickoo

Western Thunderer
Just as an extra to all this, my recent etch back from PPD was massively over etched, three sheets of junk really.

Material was 0.40 mm, slot on the drawing was 0.45 mm, PPD recommend 1.2 times material thickness so it should be 0.48 mm technically. The slots came back 0.65 mm wide :eek::rant:

A couple of half etch panels were gauged up, they should be 0.20 mm thick, they're in the region of 0.14 mm.

The bit that is bugging me is that four weeks ago, the same etch (previous test build) was near perfect and none of these parts have been touched, though there were other corrections on the sheet.

It's the inconsistency that's screwing me about, keep to one procedure and I can work around it.

I'm going to add a new line of text, DO NOT OVERCOOK.
 

neaston

Western Thunderer
The odd occasion I have had a problem with etches from PPD they have redone them for me at no cost.
It has only happened on a couple of occasions over many years.
But it does demonstrate an inherent inaccuracy in the etching process.
Nick
 
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