fusion 360 – Page 9 – Woody's Workshop

March 21, 2019February 25, 2021

A Mini Vacuum Clamping Table for PCB Engraving

You know only too well how I keep on going on about FlatCam and milling printed circuit boards on the Tormach PCNC440.

You will also have read about my preoccupation with trying to hold the PCB material flat to avoid variations in milling depth.

I have got it to a reasonably repeatable process using mechanical clamping but you know when a perfectionist starts something it has to be as good as possible …. step forward the Vacuum Clamping Table.

The thinking for this followed on from the Rosebud Grate experiments on my live steam locomotive. The grate consisted of a matrix of larger holes on the underside of the grate leading to a small bore hole on the top side of the grate. The theory as I understand it was that the reduction in size creates a Venturi type effect and boosts the air stream into the fire. I wondered therefore if I reversed the air flow i.e. sucked the air from the large hole into the small hole whether this would be beneficial in providing a boost of the suction. It is a bit tenuous I must admit and I can’t point to lots of science to back this up, but certainly worth a play.

First stop was Fusion 360 and a two part plate was designed. This consisted of a top and bottom part. The bottom part is 15mm cast aluminium with a milled trough and the top plate is 10mm cast aluminium with 6.8mm holes (no science – this is tapping size for M8 that was already in a Tormach collet) on the top side that reduce down to 1.3mm holes (ditto also already in a collet) as breakthrough holes on the bottom surface. Around the edges are M6 screw holes to clamp the two plates together and also M8 mounting holes to fasten the plate to the tooling plate on the Tormach. I didn’t quite think the suction connection fully. After I had worked out the total area of the 1.3mm holes I realised that to accommodate this I needed a 16mm diameter hole for the air inlet. This was not going to be possible to mount on the 25mm overall edge of the plate. The solution was to 3D print a connecting pipe and mount this on the top surface. This adapts to the vacuum cleaner pipe being used as the suction source. The 3D printed adapter did not provide a good seal to the top plate so I had to fit a rubber gasket on it. The parts were all put together as shown below.

Finished vacuum plate on test in the bench vice

Close up view of the 6.8mm blind holes leading to 1.3mm through holes

To my amazement it seems to work !

There does not seem to be leakage on the joint between the two plates and the vacuum pipe adapter with the rubber gasket seems to seal alright. If I put a large piece of PCB material over all the holes it is very difficult to move it. Single sided board is naturally bowed in the manufacturing lamination process and I can see it visibly jump flat when I turn on the vacuum. If the PCB is smaller than the total area of suction holes it does not seem to matter about covering over the ‘non-used’ holes to maintain the grip.

Proof will be when I try to run a board.

The milling process will not have major sideways pressure as the depth of milling is quite small so it should be fine. Clearly I can’t go drilling the component mounting holes in the PCB material with this holding technique but I can spot drill them to say 1mm depth and then finish them by hand having got a guide hole to start me off.

But all this will have to wait as the X axis limit switch has come apart on the Tormach and a spare has been ordered and is on its way.

UPDATE Feb 2021 – Flatcam and milling pcbs 2021 pdf download

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February 5, 2019February 5, 2020

Stretching FlatCam and PCB milling on Tormach PCNC440

Tormach M Code Expansion Card

I have got a project underway to use the Tormach USB M Code expansion board in association with an A axis rotary table. Details of this will follow in due course. The expansion card when added to a Tormach mill allows the operator to embed M Codes in their CNC program which will operate up to 4 dry contact SPCO relays or accept 4 inputs as handshaking acks.

My Cabling Masterplan

As part of this project I need to have cables from the USB expansion board to various devices and in a rush of blood to the head decided to use standard readily available Micro USB cables for this. Now the cable connectors are pretty small and the PCB mating socket is even smaller with its 5 connections. Glibly overlooking this I asked a colleague to produce a PCB layout for the connector to a breakout connector strip. Dave duly produced a layout and a scratching of head resulted. How was I going to produce the PCB and how was I going to solder to the connections assuming I could see them ….

FlatCam to the Rescue

Elsewhere in my blog there is mention of the use of FlatCam to create a CNC GCode listing from PCB Gerber and Excellon files. This program works really well and many successful PCBs have been produced but I have never attempted to mill such fine PCB tracks. A number of problems needed to be addressed to make this successful. The PCB sheet needed to be held very flat on the PCNC440 tooling table and the correct milling tool with its associated feeds and speeds needed to be chosen. In the past I have used strips of aluminium to fasten the PCB blank down on the tooling table. This is never perfect and leads to variations in the pressure around the edges of the board. With single sided PCB there is a natural curvature of the board material as a result of the surface tension of the laminating process. A single sided blank has a concave surface on the copper side. I needed to create something more repeatable.

Milling Window Restrictions

Before I bought the Tormach PCNC440 I had a discussion with John Saunders at NYC CNC and he recommended going for the biggest machine I could fit in my workshop. I could have squeezed the 770 in at a push but I would have had to sell off my Myford VMB which I was reluctant to do. My order therefore went through as a 440. With hindsight this decision has been justified on two counts. I rarely need a larger working area than the 440 offers and the VMB gets used very regularly for quick jobs that don’t justify CNC. This project was an exception. I wanted to make a frame that would clamp the PCB blank down onto the tooling table. In order to get the maximum working area for the PCB blank the clamping frame would have to sit outside the machining area. How was I going to manufacture it ? Fortunately my tooling plate was designed to have a mix of M8 clamping holes and 3.7mm tooling holes and I was going to use this to advantage. The clamping frame would be symmetrical. By adding some matching tooling holes in the frame I could cut just over half of the frame and then flip it round 180 degrees and cut the second half. Here is a picture of the CAD showing half of the machining on what will be the underside of the plate when in use. The outer holes are for the M8 clamping to the table and the four smaller holes are the tooling holes. Being tight with my materials I did not want to just mill out the centre of the plate and have a mountain of swarf (chips). Instead I designed it with two slots as shown, one for the clamping surface and one that almost cut through the stock. The partial cut was to ensure the central piece did not flip out once cut free and damage my cutter. First one half was drilled and cut and then the plate was rotated 180 degrees and the second half cut. This left the central island just held in place by less than 0.5mm of material. This was easy to hand cut through to liberate the central area. The plate was then turned over and the cut edge cleaned using the same tooling position and doing the same 180 degree rotation. To my surprise the rotation process on the tooling pins worked very well with only a minor step transition at the overlap point on all cuts. This was probably more down to my 3.7mm tooling pins being not quite concentrically turned from 4mm silver steel. With this finished I now had a much more robust clamp for the PCB material. I had made the clamping step 4mm deep so I could put sacrificial backing boards behind the PCB being run. This would allow drilling through as needed. Checking the flatness of a clamped PCB blank with my Haimer showed variation of a few thou in the top surface of the PCB Z position. The worst case variation in Z was at dead centre where the PCB’s natural bow was most dominant.

Tooling and Feeds and Speeds

The next problem was the milling tool and feeds and speeds. I experimented with various V shaped routers but was not happy with the results. The 5 thou tip on a 10 degree V tool was incredibly fragile. Also because the tool was V shaped, any residual bow on the PCB surface lead to a variable width cut. In the end I opted for Think & Tinkers 15 degree, 2 flute tapered stub (P/N EM2E8-0051-15VC). This has a 5.1 thou cutting tip which is parallel for the first section so depth variations have no impact on the width of cut. I ran the program at 10,000 RPM (PCNC 440 maximum) and at 150mm per minute feed rate. The PCB does not look particularly beautiful after milling as there are burrs and shavings present but a gentle rub over with a fine wet and dry removes this and leaves a remarkably clean cut tracking. The images below show some of the results. The fine tracking for the USB connector connections is shown on the microscope with a scale for reference. This shows the five fingers occupying 120 thou with fairly similar track to gap widths of around 15 thou. So now I just have to solder the connectors in place …. I will let you know how it goes.

Overview shot of the clamping plate in position on the my tooling plate on the PCNC440

Finished clamping plate in position on the Tormach PCNC440 holding down a 6″ square piece of single sided PCB.

Tracking on the USB micro connector mounting

Zoom shot on the USB connector tracks with the graticule giving an idea of scale (small divisions are 0.5mm)

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January 1, 2019January 8, 2019

Fusion 360 Speeds and Feeds

It has been a quiet period leading up to Christmas and it has lead to some low level activity catching up on items on the ‘Things to Do’ list.

One of these was to make a graphical representation of what the Fusion 360 Feeds and Speeds dialogue box means and the calculations behind it. To be honest this tab in the Fusion CAM section used to frighten me but I have become more confident with it. The problem is I can’t remember what each box affects so here is a visual representation which might help others. Note that the dialogue changes between a ramp into the stock (such as when cutting a pocket) and a plunge into the stock (such as when drilling).

I hope that makes sense and I have got it right. It certainly helps me to understand what is going on and the calculations going on in the background.

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October 19, 2018October 20, 2018

Hawaii, Combine Harvesting and Alibre v Fusion 360

Hawaii Ironman and Seattle

Having got home from Chicago I had a few weeks at home before we left for Hawaii where my son was participating in the Ironman World Championships. This is a crazy triathlon event in 30 degree heat and he finished in just over 9 hours.

We played a few rounds of golf on the Makalei course on Hawaii which is at 2500 feet above sea level. Sometimes in sunshine, sometimes cloud and sometimes hissing down with rain all of which made it challenging. We also visited Pearl Harbour which was quite moving and this included visiting the Aviation Museum on Ford Field.

No visit to Hawaii by a Brit would be complete without a visit to the Captain Cook monument in Kealakekua Bay. We completely misjudged the arduous terrain we would experience in getting down to the monument and nearly came to grief with dusk fast approaching.

Captain Cook Monument Inscription Plaque in Hawaii

On the way home from Hawaii we stopped over in Seattle for a few days which was a culture shock on body temperature. We visited the Pacific Science Museum and the Space Needle plus a tour of the Boeing works as part of the stay. The PSM is brilliant for kids (and OAPs).

All in all a good trip but will now be glad to get back in the workshop.

CAD & Farming

Being away home and more precisely away from the workshop, allowed me to do a few write ups that might be of interest and both of which were stimulated by reading forum posts on MEW. My waffle would have been too long to post in the normal way.

The first write up is about CAD/CAM and my concern that there will probably be unfilled expectations from the news about Alibre doing a special deal for MEW readers.

To 3D CAD or Not

The second write up is about harvest time in North Yorkshire that is based on my younger days in a farming family. This has been on the stocks for some time and the posting on the forum kicked me into finishing it off.

combines and harvest

Hope you enjoy these two missives and more proper stuff from the workshop soon.

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September 11, 2018September 12, 2018

NYC CNC at MHUB Chicago

Rather than have the annual Open House at his factory in Zannesville, John Saunders at NYC CNC decided to have a joint event in Chicago at the MHUB facility under the banner of a Manufacturing Entrepreneurship Summit.

The format was for key presentations together with the attraction of having a tour of the MHUB setup which is a resource facility for product development.

John Grimsmo, a highly respected knife maker, told of his ups and downs prior to his current success. This was followed by Jay Pierson telling his not dissimilar path to his company’s success in the machining work holding market.

After a break for a tour of the facilities there was an update from AutoDesk regarding developments on their wide portfolio of engineering software with particular interest in Fusion 360. There was then a closing Q and A session.

The tour revealed the breadth and depth of the resources available to external organisations at MHUB to help get a product to market. An extensive mechanical workshop, 3D printing, electronic workbenches and software development are just a few of the tools and resources available. It was impressive.

The afternoon and evening passed quickly and it was good to see some familiar faces from my visit to last years Open House and the training course I attended in Zanesville.

John Saunders in checked shirt flanked by Jay Pierson, John Grimsmo

As I sat listening to Jay and John I could not help but identify with how they had got to where they are and the parallels with my business days. We may be many years apart but we have all suffered the same ups and downs, long hours etc that are an essential part of getting to success.

An excellent event.

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