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Nthkentman
22-08-2014, 10:36 PM
Hi Guys

As I will be cutting out shapes in 4mm MDF, which to prevent them snagging the cutter or being damaged I am machining in "Nibs" at half depth and 2mm long.
When the shapes are pressed out of the main board there are obviously small sections that need finishing.
Currently my thoughts are a bobbin sander.

Has anyone any suggestions or recommendations for a reasonably priced and quiet(ish) one?

Looking at the Triton ones on eBay at the mo

EddyCurrent
22-08-2014, 10:42 PM
If the parts have concave edges then a bobbin sander will be fine but if they are straight or convex you might be better with a small combined disk and belt sander. I'm thinking the bobbin could easily create indentations in the edges even if you went careful.

Nthkentman
22-08-2014, 10:52 PM
I see where you're coming from Eddy, the edges will vary, depends on what I am producing, words, letters, shapes, all with differing edge profiles.
I was aiming to reduce the need to sand, turn over, sand again situation, but perhaps a small belt and disc sander may be a way forward



If the parts have concave edges then a bobbin sander will be fine but if they are straight or convex you might be better with a small combined disk and belt sander. I'm thinking the bobbin could easily create indentations in the edges even if you went careful.

EddyCurrent
22-08-2014, 11:33 PM
Sounds like you need both :eagerness:
The biggest problem I have with bobbin sanders is bobbins, the price I mean, it can get expensive. So I use these in a drill press; http://www.axminster.co.uk/axminster-sleeveless-sanding-drums
It means you can use strips of regular abrasive from a roll, much cheaper.

GEOFFREY
23-08-2014, 12:34 AM
I think that you can afford to leave your tab much thinner, If I use tabs I only leave about 0.5-0.75 mm thick material to cut away,
this is easily done with a scalpel. Not much "cleaning up" at all. Do not try to brake the piece out as this makes more work. G.

Of course this applies to small pieces in thin material (4mm mdf 2mm cutter). G.

Nthkentman
23-08-2014, 08:04 AM
Sounds like you need both :eagerness:
The biggest problem I have with bobbin sanders is bobbins, the price I mean, it can get expensive. So I use these in a drill press; http://www.axminster.co.uk/axminster-sleeveless-sanding-drums
It means you can use strips of regular abrasive from a roll, much cheaper.


OOOOH !

Now *that's* an idea I like....Having only a few days ago purchased said small pillar drill !
Nowt fancy, but a useful, (Even more now) tool.

Thanks Eddy

Nthkentman
23-08-2014, 08:08 AM
I think that you can afford to leave your tab much thinner, If I use tabs I only leave about 0.5-0.75 mm thick material to cut away,
this is easily done with a scalpel. Not much "cleaning up" at all. Do not try to brake the piece out as this makes more work. G.

Of course this applies to small pieces in thin material (4mm mdf 2mm cutter). G.

Hmmmm,

I'll have to experiment. I see your point about depth though.

Safety wise.... I'm unsure about having SWMBO using a scalpel... Might give her ideas !
:untroubled:

JAZZCNC
23-08-2014, 11:04 PM
If your just cutting out largish shapes on regular basis and know roughly where they will be on table then think about Vacuum pods.? Pods not bed.
With vacuum pods you can positon them so they hold the material such that the vacuum seal is never broken so needs little vacuum (Henry will easily hold) and they hold the part clear of the bed so you can profile all the way around at full depth.

EddyCurrent
23-08-2014, 11:16 PM
. . . think about Vacuum pods.? Pods not bed.

But they seem reluctant to show a price, unless I've not found the right place yet.


Make your own !

http://www.trend-uk.com/en/UK/product/MMACH_KIT/4/332/minimach_u_mach_user_make_kit_.html

JAZZCNC
23-08-2014, 11:40 PM
But they seem reluctant to show a price, unless I've not found the right place yet.


Make your own !

http://www.trend-uk.com/en/UK/product/MMACH_KIT/4/332/minimach_u_mach_user_make_kit_.html

What I never mentioned any company.? . . . . . I meant to make them not buy them.!

HDPE or any plastic is perfect, chopping boards from 1 shop are great. Just route groves for neoprene gasket and hole for vacuum and away you go.

JAZZCNC
23-08-2014, 11:43 PM
Here you go Eddy just like this. . . .Simplizzz.!
http://www.veneersupplies.com/products/Podz-Vacuum-Clamping-Jigs.html

EddyCurrent
24-08-2014, 09:35 AM
Looking at both bought and home made, I wonder how accurate they are. For example you have a piece of aluminium, say 300mm square, it's even thickness all round, you mount it on the pod, then do an engraving cut at 0.2mm all over the surface, will it work ? Also keep in mind it's no good skimming the surface because then the stock will be of uneven thickness and in some cases this will matter.
One aspect is the gasket, with it being of flexible material it will 'give' due to Z downward pressure.

GEOFFREY
24-08-2014, 11:32 AM
Eddy, once sucked down there should be no further "give". The gasket compresses and just forms a seal. However I do not think that PODZ is the answer as I imagine that with profiled alphabet letters nos. etc. it would be very difficult to be able to cut right through without damaging the pod as the items are likely to be quite small. "Tagging" does work very well, and nib/tab/tag removal is very easy. Double sided tape does work ok, but if there are a lot of small components it means a lot of tape to apply and remove. G.

EddyCurrent
24-08-2014, 11:44 AM
. . . However I do not think that PODZ is the answer . . .

I suppose you could leave a skin but then you're back to the removal of it. Of course custom vacuum pods would work if they were shaped for each item to be cut, like this;


https://www.youtube.com/watch?v=GU5vCg0EszM

JAZZCNC
24-08-2014, 11:59 AM
However I do not think that PODZ is the answer as I imagine that with profiled alphabet letters nos. etc. it would be very difficult to be able to cut right through without damaging the pod as the items are likely to be quite small.

Yes agree Geoffrey that's why I said if largish shapes. I built a machine for someone who uses it for letters etc and they use DST but it is a pain to them and a vacuum bed to hold small parts is out the question due to size of setup required as you know.
Tabs are good but again cleanup required so time.!!. . . . . It's a challenge but if was so easy everyone would be at it, which they are starting to be.!. . . Lol


Looking at both bought and home made, I wonder how accurate they are. For example you have a piece of aluminium, say 300mm square, it's even thickness all round, you mount it on the pod, then do an engraving cut at 0.2mm all over the surface, will it work ?

In this case eddy you have them pull down to the POD surface (It's a differant setup to what I posted but same setup as I described with cutting groves and using gasket) and the gasket just forms the seal. The trend setup and the PODZ style of pulling to sealing tape is only any good for wood use really where that level of accurecy isn't required.

Nthkentman
25-08-2014, 11:01 PM
eBay item 191260263022
Looks promising,,,,

Mind you I really need to get practicing now I have the machine home.

Could do with some simple pointers and info on Zero points for work and axis etc.. I've forgotten more of what I learned 35 years ago than I thought

JAZZCNC
25-08-2014, 11:58 PM
Could do with some simple pointers and info on Zero points for work and axis etc.. I've forgotten more of what I learned 35 years ago than I thought

It's simple really.!! . . . .You have 2 coordinate systems to work with.?. . . . Machine coordinates and work Coordinates.

Machine coordinates are the area of your work envolope. Machine Zero is defined by referencing the Machine to switches. This is known has the HOME position.
From this Home reference point you can acurately find any point or work coordinate on the table.

Work coordinates are Defined by selecting a point on your work material and setting ZERO point. This Zero point will be the Zero point you set in Cad and you'll use this as a refernce to where on the Work material you'll place it.

Now the work material can be anywhere within the Machine coordinate enverlope and the WORK ZERO is always known by it's distance from the MACHINE ZERO.
So if you cock up or snap a tool etc and lose position then you can always accurately get back to WORK ZERO or any position in the WORK coordinates by sending the machine to the HOME position so it references to the switches again and resets the MACHINE HOME position. From this reference point it can find any other point on the table.

Taking it a step further You can have WORK OFFSETS. Essentially OFFSETS are the same as breaking the table into smaller individual WORK areas each with it's own ZERO point.
Most people don't often realise it but they are working in an OFFSET, it's G54 which is default WORK OFFSET. They define this every time they ZERO for the part.
But you can have Many OFFSETS each with there own unique ZERO point within the MACHINE coordiante system. These are given OFFSET numbers starting at G54 then G55, 56, 57 etc and depending on the control system there can be upto 255.
You set these WORK OFFSETS up in the control system by specifying MACHINE coordinates for each OFFSET Number. Then when the control software comes across this OFFSET number in the G-code it knows where to go in relation to MACHINE coordinates to find WORK ZERO for that OFFSET.

OFFSETS can be very poweful when used correctly and are great if you use fixture jigs. Each Jig could have it's own differant part with differant material and still be cut in the same G-code file in one go.

This getting little deep now but to recap.

Set Machine Zero by sending machine to HOME position. Then throw material anywhere on table and Define ZERO WORK position by Zeroing the DRO's on the screen or selecting WORK Zero some where on the material.

That's it really the part will be cut in G54 OFFSET (Check your G-code file and near the top you'll see G54, if not specified control system will default to G54) and ZERO point for the WORK will be where selected on the material.

The control system keeps track of the rest and after HOMING will accurately get you back to any lost WORK position if needed.

Nthkentman
06-09-2014, 10:09 AM
Well, at that price I've given it a punt... Now to persuade the router to cut a nice neat series of slots for the gasket in a suitable sized 19mm ply or MDF board big enough for a multitude of sizes etc.
Having a good old Henry vacuum I feel some engineering needs doing to make adapters to plumb it all together.... Now where *is* my good mate Mark (A toolmaker) hiding.....



But they seem reluctant to show a price, unless I've not found the right place yet.


Make your own !

http://www.trend-uk.com/en/UK/product/MMACH_KIT/4/332/minimach_u_mach_user_make_kit_.html