cnc milling – Page 8 – Woody's Workshop

March 31, 2019April 2, 2019

Improving and mounting a low cost chuck from Sanou for wheel cutting

I am still building up to automated wheel cutting on the Tormach.

I have mounted the Sherline CNC rotary table on my tooling plate and the table now needs a chuck or collet mounting plate fitting. This will grip the super glue arbors that I use for holding the wheel blanks while cutting.

I decided a chuck would be the best option and bought in a low cost 80mm three jaw chuck made by Sanou. These are available from a number of outlets on EBay. It is supplied with internal and external jaws and a chuck key.

It arrived very quickly and felt horrible. Turning the chuck key was really gritty and jumpy. Rather than sending it back I decided it would be worthwhile stripping it down to see what was going on.

I have never attempted stripping down a chuck before and to my surprise it was relatively simple. I first removed the three jaws, then the three rear cover retaining screws, the three adjuster retaining pins and finally the three adjusters. In theory then the spiral plate should drop out. But it didn’t and it took some serious tapping with a soft tool to remove it.

Having got all the bits apart and in front of me I began to deburr all the sharp edges that I could find. What seemed particularly important was to clean up the spiral plate internal diameter as this seemed to be the tightest fit. A flat diamond coated file together with a triangular one were the best tools to use. Once all this was done I put all the parts in the ultrasonic cleaner with hot water and detergent. There was a surprising amount of grit in the bottom of the tank once cleaning was finished.

Re-assembly was the reverse with everything being coated with moly grease before assembly. It was now a completely different chuck. Beautifully smooth.

The next problem was mounting the chuck on the CNC table. I first made a mounting plate with three M6 clearance and counterbored holes on the PCD mounting holes for the chuck (66mm) and four M5 clearance and counterbored mounting holes to match the cross slots on the CNC table (96mm). I also put a 16mm clearance hole in the centre of the disc to match the chuck bore. Next problem was how to centre the chuck on the rotary table. Fortunately the rotary table has a central, tight fit 11mm (0.25″) shouldered hole leading to a UNC 3/8″-16 screw thread. This is the mounting for use on Sherline products. I cut the UNC thread on the end of a piece of 11mm silver steel and screwed this in place at the centre of the table. This was perpendicular to the table face.

I then fitted the chuck to the backing plate and lowered the chuck and plate assembly over the 11mm rod and loosely tightened the jaws. This allowed the chuck to just rotate so that the four table slots could be aligned with the four holes in the mounting plate. These four screws were also loosely tightened against the T slot nuts and then the chuck pushed firmly down and the jaws closed tightly. The four table mounting screws were then tightened. The chuck should now be centrally placed and tightly in position.

Sherline CNC table mounted on the Tormach tooling plate with the Sanou chuck on its mounting plate and with a super glue arbor in the chuck. The controller for the Sherline table is shown which was designed by Bryan Mumford who also designed the Microset Clock Timer. The weird plate on the Tormach tooling plate is a lump of scrap steel for my dial gauge magnetic base to attach to. You can just see a cutter in the Tormach slitting saw arbor at the top right.

The 11mm silver steel centralising rod could be unscrewed and removed. I put a piece of 20mm silver steel in the chuck jaws and checked the run out as being +/-0.05mm which to me didn’t seem bad and more than adequate for the task intended.

A new experience and a good end result.

Still got the GCode to sort out to automate the process … and finish off the USB expansion unit to increment the motion controller.

Update : –

I found that just a straight 11mm rod with a 3/8″- 16 UNC thread on the end was not reliable in sitting square to the CNC table surface. This resulted in the chuck running eccentrically. I modified the centring rod to have a collar fitted (16mm diameter to clear the chuck central hole) which was silver soldered in place and then trued up on the lathe. This modification allows the chuck to be fitted and centred easily and quickly each time. Here is the Fusion 360 model.

Chuck centring rod (11mm diameter silver steel) with a 3/8″-16 UNC thread to fit into the Sherline CNC Rotary table central mounting hole and with a collar to pull up against the rotary table face to keep the rod true. The M6 hole on the rod end is for a cap head screw held in place with Loctite. This allows easy release of the rod from the rotary table once the chuck is in place.

I also added a M6 threaded hole in the end of the rod to allow the fitting of a cap head screw. This is Loctited in place and is used to release the rod from the rotary table central threaded hole once the chuck is in place. An alternative would be to mill a hex head on the end of the rod but I took the lazy way out.

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March 26, 2019June 30, 2020

Clock Wheel Cutting Adaptation of a Tormach Saw Mandrel

I am slowly building up to being able to cut wheels on the Tormach PCNC440 with two possible methods.

The first is using Gearwheel Designer which is mentioned elsewhere on my blog.

The second route is more conventional using a PP Thornton or similar cycloidal tooth cutter and a dividing device on a rotary table. This later method is how wheels are traditionally cut in a lathe and there is a lot of information available on this.

In order to use the cycloidal cutters I need some form of arbor to mount the cutter in the Tormach spindle. I could simply turn a piece of steel bar to suit and mount this in a ER collet in the spindle. The downside of this simple approach is that every time the arbor was fitted into a collet the cutter would be at a different height from the table. I really wanted something a bit more repeatable as the centre line of the rotary table will always be the same so why not the cutter centering.

When I ordered the Tormach PCNC440 I also ordered the Tormach small rotary saw arbor (which to date I have never used). Pondering this last night I sketched up an adapter in Fusion 360 to allow an involute cutter to be fastened to the end of the saw arbor.

This is shown below. It is made from a piece of 19mm AF hexagonal steel bar with the hexagonal flats going to be used as a tightening it in place in the Tormach arbor. My Myford Super 7 when used with a 3 jaw self centering chuck is not bad on concentricity but for really accurate centering I swap the chuck for a collet face plate instead. This job was going to need both.

First operation was to turn the hex bar end that would screw into the arbor. This was done in the lathe chuck. It was a simple turn to a diameter and drill and tap the end with M6 to match the arbor mounting. The only pain was the arbor has a slightly protruding lip so I had to undercut the mounting face for this. Rather than trying to be clever I did it by hand using a graver.

While the hex stock was still in the lathe I roughly turned down the other end of the adapter to the primary diameter and slightly oversize for the cycloidal cutter bore diameter and then cut off the stock so far.

It would be important to get the cutter mounting running as square as possible so I swapped the lathe chuck for the collet plate and mounted the arbor end of the adapter in the collet. I carefully turned the shoulder for the cycloidal cutter diameter and then reduced the remaining length ready to cut a M6 thread.

Here are a couple of images of the finished adapter.

Tormach TTS saw collet with my adapter and a typical clock wheel cutter

I am pleased to say the idea went almost to plan and it runs very true in the Tormach spindle.

I was a bit over enthusiastic with the graver but this is of no consequence.

With hindsight the shank between the cutter and the hex section ought to be longer as this will restrict the diameter of the wheel that can be cut before the blank catches the hex section peaks.

One step closer to trying this method. The next experiment is to work on a sub routine in GCode to move the cutter back and forth while cutting and with the ability to easily program the number of cuts.

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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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February 1, 2019

Tormach PCNC440 Bellows Protection

The Problem

It has been one of those things that has been nagging for some time….

I have had a couple of frights while severely destroying metal which were brought about by the rear Y bellows on the Tormach having got filled with swarf (chips). The machine had tried to do a severe Y movement to the rear of the machine and the bellows began to try to crush the swarf (chips) that had accumulated in its grooves. While it may not do any fundamental damage it does sound awful and does give rise to a transient expectation of an underwear change.

Some time ago I had ordered in some 1mm Nitrile rubber sheet to solve this problem and it had been sat gathering dust waiting a “non busy” day. Today was that day. Time to sort this out.

The Nitrile sheet I had ordered in from EBay was 500mm square. When cut down the middle it would nicely span the bellows. I also had some asymmetric profile plastic angle section measuring 30mm x 20mm x 1mm which had been brought back from the Brico in France. (For me the French Bricos are a regular source of material as their range of aluminium, steel and plastic sections far outshines our UK DIY stores).

The Method

I cut two lengths of the plastic angle at 250mm long to match the Nitrile, one for the top of the Z axis bellows and one for the table end of the Y bellows. On the shorter arm of the each piece of plastic angle I put 5 x 3mm clearance holes and marked these though onto the rubber sheet. I cut the matching holes in the Nitrile sheet using a rotary punch. I put a slight countersink on the back of the holes in the plastic to reduce protrusion down into the bellows.

The Z axis mounting consists simply of two M5 clearance holes 120mm apart on the wider arm of the plastic angle. I made these holes elongated to make adjustment of the mounting easier.

The Y axis was not so straightforward in that the two M5 bellows mounting holes into the table are set below the level of the slideway. These are spaced at 210mm. The plastic angle had to be hacked out to allow for this but this was simple to do on my Gabro notcher as the 1mm plastic is quite soft. Once again I made the two M5 clearance mounting holes in the plastic angle elongated for ease of adjustment.

The two pieces of plastic angle were fastened to the Nitrile using M3 x 5 countersink screws with a washer and nut facing out from the bellows. Rather than tighten these down hard and distort the rubber I soft tightened after adding some Loctite.

Fitting the angle to the machine is a bit fiddly as I was working blind. With hindsight the mounting holes should have been slots rather than elongated holes. This would allow the plastic angle to be slid into place without taking the bellows screws out.

The 500mm length on the Nitrile seems just about right as it does not bulk up too much at extreme table positions. A little longer perhaps but no shorter. The 250mm width gives plenty of overlap across the bellows to keep them clear of swarf/chips.

I am pleased with the result and I am sure long term my underwear will also benefit. Below is a guidance sketch of the plastic angle details and a few finished shots of the Nitrile in place on the Tormach PCNC440.

Bellows protection on Tormach PCNC440 using Nitrile sheet — Plastic angle dimensions for the Z and Y axis bellows Nitrile cover mounting

tormach, bellows protector — Z Axis bellows protector sheet top mounting on Tormach PCNC440

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