machining Aluminium 5028 plate

I have been asked if its possible to come up with a design for a measurement Jig for measuring Dagger Boards used on Cadet sailing dinghy's by my club

The plate would need to be approx 25mm thick by 300mm long by 250 wide

It will need to have 2 slots machines into it approx 150mm long by 15mm wide narrowing to 3 mm radius at each end

on the opposite side it would need a portion removed and radius at 150 mm so it could be offered up to a radius on the dagger board to check its profile

The slots I can probably do but how to machine the recess at a 150mm on the back

1. without causing any distortion

2. achiving such a radius

I have a warco WM16 mill with extended table and a basic rotary table

Lastly is the Aluminium the best material

Any advice greaty appreciated, I should say this will be going with our cadet youth sailing fleet to the world championships in Melbourne Australia this december and is to be used just as a quick check jig nothing official

Thanks

Trevor

Edited By Trevorh on 09/08/2022 10:10:07

5028 is an unusual choice. Isn't that a wrought ally with magnesium in it and not overly machinable? More common 6061 T6 is my "go to" ally.

I can;t visualise what you wish to machine from the description. A drawing or pic of similar item would be most helpful.

Hi Hopper,

Just trying to sketch it now and upload it

Basically imagine a pencil the same shape at each end but about 150mm point to point and 15mm thick

so a slot whoch tapers at each end down to a 3mm radius

then on one side of the plate/bar a relief machined into the it at a 150mm raduis to enable you to offer up a "disc" to check its at the correct raduis/diameter

turn the disc on its end and see if it drops through the slot

I hope to have the sketch soon

regards

Trevor

Ok so here is the sketch apologies for my poor attempt to show what I am trying to achieve

If you can come up with an accurate slot shape it would be a simple job for CNC, the sketch as drawn does not have sufficient detail. Also if you could define what is being measured it may help.

Martin C

I think you could machine that radius with an end mill cutter and mount the job on a larger plate on top of your rotary table so you could achieve the 150mm radius. Or mill the whole thing out of a larger piece of plate that can be bolted to the rotary table with 150mm offset, then cut the plate down to size afterwards.

The slot would be straight forward slot milling for the main part then do the ends with a 6mm cutter to give your 3mm radius at the tip, again using rotary table to get the angle of the pointed part of the slot.

Here is a photo of a dagger board that I need to be able to measure its bottom radius as well as its width, thickness and tapered edges

Thanks Hopper

The material you mentioned - who would you suggest to get it from?

If the slot is 150mm long then does the radius not need to be 75mm rather than 150. in which case just about swingable with a boring head.

6062 available from most hobby suppliers such as M-machine

Edited By JasonB on 09/08/2022 11:44:56

Hi Jason

Yes your correct - I am just waiting on the sailing club to confirm whether its a Raduis or Diameter they want

Once I know this I can determine the length of the Plate /Bar and its width

Thanks for the advice Guys

appreciated

trevor

Likewise you say 3mm rad for the slots in the first post and show 3mm dia on the drawing, that's a long reach for a small dia cutter.

Wonder if one of the plastics may be an option, at least it will float if dropped.

I would think a simple plate with a slot, as used in the post office for letters, would allow the profile to be checked easily. A simple plate with three dowels in it would allow checking of a radius/diameter. If all three dowels contact the part then the radius is correct, if the centre one does not touch the radius is too large, if one of the outer dowels does not contact the part the radius is too small. It does not need to be a huge plate, something like 75mm between the two outer pins would be enough.

Here is what I mean, it uses far less material than a large plate and is easy to produce.

Martin C

Edited By Martin Connelly on 09/08/2022 12:17:46

I'd use Delrin or similar for the profile gauge.
If you use metal make sure the edges are rounded and inside polished. I could foresee trouble if it scratched the varnish on someones board......

Robert G8RPI.

Hi Guys

These are all excellent ideas and quite valid and I must admit I wasn't sure How I was going to polish or protect the boards as they were being measured

as Jason and Robert say maybe look at different materials as long they can hold a reasonable tolerance +/- 0.5mm then all good

The idea of Dowels by Martin would certainly make it an easier operation and I do have DRO on the Mill so should be a reasonable operation

delrin would certainly be lighter and again is something to be considered

Once again the forum comes to the rescue - Great

Trevor

Push comes to a shove bore a 150mm dia in a square of 12mm material,on the lathe, cut in half and screw to another bit of 12mm. Cut the slot in that piece of 12mm so cutter does not have to go so deep.

Hi Jason

Now your getting creative - that way opens all new kinds of thinking and I might already have some material to hand that I can play with

I will report back, oh its definately 150mm RAD so a 320mm plate in the lathe - which will fit in my GH1240 gap bed lathe

Time to experiment

As it's only a check guage could you not 3D print it. My Ender 3 will print up to 220x220mm, so would accommodate the jig. Tolerance is pretty good <0.5mm so it would likely be accurate enough.

If it was OK you could knock off a few in case of accidents - they would come out a lot cheaper than Ali.

Something like

Cura says 128g of filament  so about £3 worth but 22 Hours printing time, however you can leave it to it.

Edited to add picture

Edited By Peter Cook 6 on 09/08/2022 14:07:46

Hi Peter,

I do have access to a 3D printer its a Prusa i3, But I dont have access to a drawing package so can't generate an STL file, but worth thinking about

thanks

Trevor

a 150 radius would give a dagger that looked like this not like the photo?

Also does it need to be a double thickness to rest against the side of the dagger or just like this offered up to the end

Edited By JasonB on 09/08/2022 15:03:55

Trevor, perhaps now is the time to grab one of the free CAD packages, or a 90day trial of one of the paid for, and have a go.

Looking at the picture in post 7, the curve at the bottom looks very close to a semicircle. So either the board is 300mm wide and the slot in your drawing (post 4) should be 300mm long - in which case the simple print idea is not going to work, or the curve is 150mm diameter.

If it is 300mm wide, you could still print the difficult bits - make 2 of these

and bolt one at each end of a length of aluminium or steel bar 

Replies go there before I finished.

Edited By Peter Cook 6 on 09/08/2022 15:37:53

Edited By Peter Cook 6 on 09/08/2022 15:40:11