cnc milling Archives - Page 10 of 14

July 29, 2018July 30, 2018

Rosebud Grate CAM and manufacture on Tormach PCNC440

While doing the drawings for the Rosebud grate on Fusion 360 I cheated slightly. From my measurements, I made a best estimate sketch of the needed grate size to fit the firebox floor and having drawn this up, I did a 3D print of an equivalent size thin piece of PLA. Having trial fitted this printed plate I did some trimming on the Fusion drawing ready to create the CAM.

I had bought in some 150mm square black mild steel plate and cut it roughly to width but left the length at 150mm this being longer than needed. This allowed me to clamp the ends of the stock to my tooling plate on a piece of MDF. I had one clean cut edge on the cut stock to use as a reference. When mounted I checked this with the Haimer to make sure it was running parallel in the X plane. Note I cut the MDF to roughly the same size as the plate so as not to interfere with the clamping.

I did a PathPilot width and length measure using the Haimer and found the centre of the plate and set this as G54. My Fusion drawing and CAM were referenced to centre. I was now ready to go.

First operation was to spot the matrix of holes and the second op was to drill them out to 4.1mm. Third op was to countersink the holes to 3mm depth. This was a bit interactive. I just worked on one hole only to start with and did repeated cuts using a BS3 countersink until the depth was correct. I then did a ‘chose similar size’ selection in Fusion CAM and then ran the full op.

This now left machining of the profile of the plate to the size of the fire box floor dimensions as per the CAM and my dummy PLA plate.

rosebud grate first operations — First Ops on the Grate, spot drilling and then hole drilling. Note the clamps on the outside of the plate area.

Clearly the clamps were now a problem as the end areas were excess material on the length. To get round this I removed the drilled plate from the MDF (the MDF had already started to degrade and swell with the cutting fluid) and mounted a new piece of MDF on the tooling plate with M8 fixings. As you will see below I went a bit OTT with these …. there is even a hidden countersink one under the plate to stop the MDF bowing upwards …

I remounted the grate on the new MDF with a single woodscrew in one of the grate holes and checked and adjusted the angle of the plate so the good edge was running true in X as before. I then added a ‘sprinkling’ of more wood screws so the plate was firmly in position and running true. I then re-referenced G54 to the centre of the grate as before.

Plate remounted on a new MDF backing plate and held in place with randomly placed wood screws using the grate hole matrix.

Now I hate making swarf (chips) of material if it is not necessary … so having got the plate securely in place on the MDF I then took it off again and cut off the excess material on each end of the length. Sad really but you never know when you might need a couple of small pieces of steel …

The grate could now be mounted back on the MDF with the plethora of screws positioning it back as before. I did re-check with the Haimer and also rechecked the Z height once again.

The CAM adaptive profiling was with an 8mm cutter. Obviously I was cutting air at each end of the grate where the stock was now missing but not a problem.

Profiling almost complete. The MDF is starting to degrade and swell.

I could have used a super glue and masking tape holding method but the black mild steel does not have a smooth surface like BMS and I was doubtful how well it would hold. With hindsight the method I adopted did give me some flexibility in the process method.

The final process on the Myford Super 7 was to make four posts to sit the grate at the correct height spacing above the ash pan to match the old bar grate position. These posts were fixed onto the grate by sacrificing four of the holes. This of course reduces the hole count and therefore the hole area percentage occupancy from 15.17% to 14.62% – but not worth worrying about.

Finished grate standing in the ash pan and also the 3D printed test shape

So now I have to prove that all this effort was worthwhile and the grate will make a difference to the Polly V steaming. More to follow on this in due course. We have had some rain over the past couple of days so the Club track will no doubt be open for steaming in the near future.

Similar or related subjects : –

July 26, 2018December 1, 2021

Rosebud Grates for Live Steam Locomotives

The Rosebud Phenomenon

I recently had a discussion with a fellow model club member about fitting a Rosebud grate to a Polly V locomotive. There is quite a lot of discussion on various forums of this style of grate so I won’t repeat what has already appeared in the likes of Model Engineer. The gist of the design is to replace conventional live steam bar type grates with a plate having a matrix of holes with back countersinks such as to occupy around 15% of the grate area. The effect of this change is to get better combustion of the fuel and better efficiency. Most users report only a fine powder residue after steaming and have observed that the fire appears to ‘float’ on the plate surface. The back side countersinks appear to create a sort of Venturi effect to boost the draught to the fire.

How to Calculate the 15% matrix

So all this got me thinking. This would be an easy job to run on the Tormach and all I needed was the design entering on Fusion 360. Which brought me round to the calculation of the 15% surface area for the holes on the new rosebud plate. Those who know me will bear witness to my weakness for doing spreadsheets and this little problem suggested a spreadsheet was needed.

Below is a simple sketch of a rosebud fire grate with dimensional attributes. In the calculation I have allowed for a border around the holes in case there are any no-go areas for the hole matrix. I have now updated the spreadsheet to allow holes to be ignored such as where used for mounting pillars. I also give the XY coordinate of the corner holes relative to material centre to help the machining layout.

Below is a screen shot of the resulting rosebud grate spreadsheet and you can download it as a ZIP file via the following link – rosebud_grate_calculator 2

Here is the finished Fusion 360 drawing ready to run on the Tormach. This shows the bottom surface with the 4mm through holes having been half depth countersunk. Clearly four of these holes will need to be sacrificed for mounting legs onto the locomotive ash pan and these are removed from the above calculation.

So all is in place ready to cut metal and I will keep you posted on the progress and steaming results in due course. (There is a slight problem at the moment in that we have a steaming ban in place because of all the dry vegetation at the club track).

Similar or related subjects : –

May 29, 2018May 31, 2018

Tormach Purchase Costing Sheet

I haven’t been completely idle while on holiday …

After I decided to buy a Tormach milling machine I had debate whether to go for the 440 or the 770. This confusion was based on available workshop space and to a lesser extent on cost. I also did not have a feel for the total cost of not just the items I needed to buy but also what the total package would cost when it landed on my driveway. In the UK we pay VAT on not just the goods but also the delivery cost.

To help my thinking I put together a spreadsheet on Excel that split out the basic machine parts and then had a common section showing all the accessories I would need. This totaled everything up in USD and I then did a conversion to GBP at spot rate and then added VAT and duty factors for UK import.

This sheet helped my enormously and once I had all the key prices loaded from the Tormach site I could do ‘what if’ calculations to fit my budget.

I was recently contacted by another potential buyer of a Tormach and I sent him the sheet to help his thinking process. For anyone else thinking of buying either in the US or an overseas country I thought the sheet might help so I have spent some time cleaning it up and and I attach the new version below.

Simply put a quantity of each item in the column associated and see the impact of your shopping list at the bottom, either as a 440 or a 770. Clearly the sheet could be extended to a 1100 if that takes your fancy. (Don’t forget to check the current pricing from the Tormach site by searching on the product code shown on the sheet).

Excel – Tormach mill costing

Don’t forget you will always need one more TTS collet than you have ordered …..

Similar or related subjects : –

May 8, 2018May 31, 2018

Mill Turning Jig

After a few distractions the Mill Turning Jigs are complete and I have run a test piece that is representative of a clock pillar.

Mill Turning Jigs

The jigs were both designed in Fusion 360. One consists of a large block with space for three 10mm cross section carbide insert tools and a second block with drill and boring related tools. I have fitted three ER16 collet chucks to this to allow flexibility of tooling choice. Both have mountings to fit onto my 25mm hole matrix tooling plate on the Tormach.

The jig manufacture was relatively straightforward with the exception of needing a new 10mm end mill having extended length (35mm) to bottom out the ER16 collet mounting holes. I got this from APT and the edges were lethally sharp.

Design in Fusion 360 — Mill Turning Lathe Tool Holding Block

Fusion 360 design — Mill Turning Drill and Boring Jig

Trial Clock Pillar

The pillar had simple geometry as below.

I opted to base this on the largest pillar I had come across in any design which was formed on a 5/8″ brass rod. I held the stock in the spindle in a 16mm ER32 collet held in a TTS holder.

I struggled a bit with the CAM for the trial as the tool geometry of the tools I recently received from Banggood were not in the standard tool library. I got some of the settings wrong. That aside the result of the first run is quite pleasing.

My feeds and speeds were a bit coarse and I cringed once or twice at the tortured sound of brass under pressure. I didn’t complete the parting off as I didn’t fancy ducking from a large piece of brass spinning lose at 5000 RPM.

Mill Turning Setup showing both Jigs in place

As ever there was quite a bit of learning while making both the jigs and running the trial pillar test piece.

Drop me an email if you want more information !

Similar or related subjects : –

March 31, 2018May 31, 2018

Tormach Post Processor G53 Edits for Tool Change

The Tormach PCNC440 is a lovely machine and is more than big enough for my present needs. The one problem I had encountered was when coming to a tool change on a CNC job sometimes there was not enough Z height to get the TTS collet out of the spindle. This was particularly difficult when using larger diameter drill bits in a chuck style holder.

Once in program there did not seem to be any option to break the run and do a G30 or similar. What I really needed was a move of the spindle upwards and outwards to get it clear of the job and allow TTS access.

Reading up in Peter Smid’s excellent CNC Programming Handbook I could see that care was going to be needed to ensure that any movement was first of all a Z action and then X and Y to avoid the danger of crashing the tool into the job or its fixtures.

I had some discussion with John Saunders at NYC CNC and John was working on a video around this subject. He helped enormously.

The end result is to use G53 machine coordinates to first do a Z and then and X and Y to move the tool up and to the side for tool change access.

This involves edits to the post processor in three places. The first two edits (Lines 44 and 66) are there to give an option for this movement in the drop down selection box. (The line 24 edit is an earlier modification to allow Mill Turning – see separate post).

tormach, post processor, G53 — Line 24, 44, 66 edits

g53 tool change edit to post processor — Change that appears in the Property selection box where the Custom Tool Change option now appears

The third edit gives the instructions for this as a G53 Z move than a X and Y move (Lines 543-538). Note that I later found that I had to add a G54 after the G53 movements as some CAM actions did not include a G54 as part of a tool change.

custom tool change edit — Line 534 to 538 edits

I later on decided it would be nice to include this G53 movement at program end so this is a fourth edit (Lines 1404 – 1405) and not forgetting the change for Mill Turning edit (Line 25) there are five changes in total.

cnc g53 tool change edit — Line 1404 to 1405 edits

That concludes the changes. I recommend that you spend time watching John’s videos on Post Processor edits on NYC CNC.

If you can’t read the edits then drop me an email and I can send you a full listing.

Note that these are changes to the Tormach standard post processor code and if you are tempted to do this you should do a ‘Save As’ on the original code and only edit the newly created and saved file so you have a fall back position. Likewise I accept no responsibility in documenting this and putting you up to potential mischief messing with your machine and causing damage.

Similar or related subjects : –