Press Fits

[IanN]

Hi,

Just to clarify the background behind the Solidworks table of fit dimensions (listed to 7 sig. fig.):

Solidworks (like all current CAD packages) uses SI units for its native dimensions - the dimensions quoted in the original table were all millimetre dimensions to three decimal places. They only become silly numbers when divided by 25.4 to convert to inches

Ian

 

[fltenwheeler]

I built a crankshaft from machined parts with Loctite 680. Two of the 8 joints have loosened up. I had the holes bored with a 0.376 reamer and the shafts are 0.375. Six of the joints seem solid and two loose. Should there have been more room in the fit larger than 0.001 for the Loctite to work properly? I did use Acetone to clean up the hole and shaft prior to assembly and I didn't touch anything for 24 hours to allow for curing. The close up shows the shaft no longer flush with the joint.
Grasshopper
View attachment 144112

View attachment 144113

What grade of Loctite did you use? I have an oddball one that I use at steam meets when someone’s wheel comes loose. It has it own primer and sets almost to fast. We had to get the torch out to remove the wheel again because it was slid on in the wrong position.

What is the optimum fit / clearance for anaerobic retaining compounds? The optimum fit for thinner / low viscosity products like LOCTITE® 603 is 0.025 mm to 0.08 mm. For thicker / high viscosity products like LOCTITE® 638, it is 0.05 mm to 0.1 mm.


Tim

 

[ChazzC]

Hi,

Just to clarify the background behind the Solidworks table of fit dimensions (listed to 7 sig. fig.):

Solidworks (like all current CAD packages) uses SI units for its native dimensions - the dimensions quoted in the original table were all millimetre dimensions to three decimal places. They only become silly numbers when divided by 25.4 to convert to inches

Ian

Yes, but - all you need to do is add a round function and format the cells accordingly.

In the 80’s I had to explain to a recent engineering graduate that even though the calculator gave an answer to 8 significant figures, based on the data being collected and utilized only the first 2 to 3 places mattered in the final answer. We lost a lot of common sense when we stopped using slide rules.

 

[davidyat]

What grade of Loctite did you use? I have an oddball one that I use at steam meets when someone’s wheel comes loose. It has it own primer and sets almost to fast. We had to get the torch out to remove the wheel again because it was slid on in the wrong position.

What is the optimum fit / clearance for anaerobic retaining compounds? The optimum fit for thinner / low viscosity products like LOCTITE® 603 is 0.025 mm to 0.08 mm. For thicker / high viscosity products like LOCTITE® 638, it is 0.05 mm to 0.1 mm.


Tim

I said in my post, I used Loctite 680 High Strength

 

[Richard Hed]

I've got 3 slide rules, and NO they are NOT for sale. In Highschool, we were taught always to estimate things which has really workt out well for me in real life. Usuaally, a real answer is within one point or at most two of an estimate.

 

[fltenwheeler]

I said in my post, I used Loctite 680 High Strength

Sorry I missed it. This is what they want.

LOCTITE® 680, it is 0.05 mm to 0.38 mm.

0.0019” to 0.0149”

Looks like the minimum is 2 thousands.

Tim

 

[davidyat]

Sorry I missed it. This is what they want.

LOCTITE® 680, it is 0.05 mm to 0.38 mm.

0.0019” to 0.0149”

Looks like the minimum is 2 thousands.

Tim

Thank You
Grasshopper

 

[ChazzC]

I've got 3 slide rules, and NO they are NOT for sale. In Highschool, we were taught always to estimate things which has really workt out well for me in real life. Usuaally, a real answer is within one point or at most two of an estimate.

My collection consists of a 6” Pickett N600-ES yellow Aluminum Log Log and a 12” Dietzgen Microglide “Decimal Trig Type Log Log” #1734 (Mahogany with Teflon lined grooves). Both have their original leather cases (without belt loops) and the Deitzgen has its plastic Conversion Tables/Trig Formulas card: “keep in your Dietzgen slide rule case for handy reference.” The Dietzgen got me through Heat Transfer until I bought a used HP 35 (it had an exponential function key), which was definitely responsible for me passing the final.

They’re not for sale either; I may will them to The Smithsonium.

 

[Richard Hed]

My collection consists of a 6” Pickett N600-ES yellow Aluminum Log Log and a 12” Dietzgen Microglide “Decimal Trig Type Log Log” #1734 (Mahogany with Teflon lined grooves). Both have their original leather cases (without belt loops) and the Deitzgen has its plastic Conversion Tables/Trig Formulas card: “keep in your Dietzgen slide rule case for handy reference.” The Dietzgen got me through Heat Transfer until I bought a used HP 35 (it had an exponential function key), which was definitely responsible for me passing the final.

They’re not for sale either; I may will them to The Smithsonium.

Ho. I took a look at mine as you inspired me. I have two Posts-one a six inch and the other a 12", a 12 K-E and low and behold a fourth one, a six incher with the name worn off!

 

[Steamchick]

Hi Grasshopper, Seriously, I wonder if Loctite has the shear strength to hold a crankshaft like yours? Maybe you need yo estimate the maximum pressure divide by the area of piston, then apply that as a torque at the radius of the Big-end and compare that torque as a shear force on the loctite... I.E. at the radius of the main journal. Consider the area of loctite in shear = the torsion as a shear force divided by the area of the loctite in shear.
In reality, you may only have half the strength the Loctite Laboratory tells you, and may have underestimated the pressure peak of the gas on the piston. I.E. Boiler + superheat pressure of a steam engine, more than 10 times compression (theoretical) if an ICE.
IF you are not happy crunching the numbers, send me the bore stroke, main journal diameter, etc. and I'll work it out for you. I have "fresh batteries in my old slide rule"... Well in at least 1 of my 3 or 4. (A couple inherited from Grandfather and Father, both a bit more worn than my 55 year old plastic one - none good enough for my local museum! - Still in use!).
Noticed a museum activity on their website "practise your handwriting in the school" as "something to discover". - I feel a "Grump" coming on!!
https://www.beamish.org.uk/explore-discover/
I notice that 2 of the LCD numbers on my Sharp EL500R calculator have lost "pixels", and it is making it harder to recognise a 5 or 6 on 1 character, or 5,8,9 on another. - Need a new calculator! - Suggestions?
Regards,
K2

 

[Charles Lamont]

Hi Grasshopper, Seriously, I wonder if Loctite has the shear strength to hold a crankshaft like yours? Maybe you need yo estimate the maximum pressure divide by the area of piston, then apply that as a torque at the radius of the Big-end and compare that torque as a shear force on the loctite... I.E. at the radius of the main journal. Consider the area of loctite in shear = the torsion as a shear force divided by the area of the loctite in shear.
In reality, you may only have half the strength the Loctite Laboratory tells you, and may have underestimated the pressure peak of the gas on the piston. I.E. Boiler + superheat pressure of a steam engine, more than 10 times compression (theoretical) if an ICE.
IF you are not happy crunching the numbers, send me the bore stroke, main journal diameter, etc. and I'll work it out for you.

Loctite is a commonly used and usually successful way of assembling crankshafts, even on model locomotive crank axles, where there are all sorts of forces involved.

While a calculation may be of interest, 'non-design' loads may well be much larger than normal ones.

With Loctited model crankshafts it is usual to pin them after assembly as a belt and braces measure.

I have never seen any analysis of the effectiveness of this measure. It may well be of benefit in increased peace of mind. Pragmatically, I think would pin.

The common practice is to put the pin hole across a diameter. It may be better to pin tangentially.

 

[Richard Hed]

Hi Grasshopper, Seriously, I wonder if Loctite has the shear strength to hold a crankshaft like yours? Maybe you need yo estimate the maximum pressure divide by the area of piston, then apply that as a torque at the radius of the Big-end and compare that torque as a shear force on the loctite... I.E. at the radius of the main journal. Consider the area of loctite in shear = the torsion as a shear force divided by the area of the loctite in shear.
In reality, you may only have half the strength the Loctite Laboratory tells you, and may have underestimated the pressure peak of the gas on the piston. I.E. Boiler + superheat pressure of a steam engine, more than 10 times compression (theoretical) if an ICE.
IF you are not happy crunching the numbers, send me the bore stroke, main journal diameter, etc. and I'll work it out for you. I have "fresh batteries in my old slide rule"... Well in at least 1 of my 3 or 4. (A couple inherited from Grandfather and Father, both a bit more worn than my 55 year old plastic one - none good enough for my local museum! - Still in use!).
Noticed a museum activity on their website "practise your handwriting in the school" as "something to discover". - I feel a "Grump" coming on!!
https://www.beamish.org.uk/explore-discover/
I notice that 2 of the LCD numbers on my Sharp EL500R calculator have lost "pixels", and it is making it harder to recognise a 5 or 6 on 1 character, or 5,8,9 on another. - Need a new calculator! - Suggestions?
Regards,
K2

In 1975, I bought my first calculator. It was a TI and cost 156.09$ (that was with tax). Today that same calculator sells for about 12$, so don't be a cheapskate. What do you want the calculator to do? Need a programmagle one? Need one with four colors? need one with sinh and cosh? Of course you wants one with graph capability. Any good one will have several memories. Enjoy looking at your various options.

As for myself, I am a calculator junkie. I have several. I lean heavily toward TI but have a four color Casio from 1992 that is a great calculator. The one thing I don't like about it is it uses those flat quarter sized batteries which are very expensive. TI uses the the cheap triple A batts. Me ythmpfks that Casios also use triple As now, but don't know for sure. What type of calculators have you got available in GB?

I got a couple cheapos (but good quality and plenty of functions) for using in my shop. However, I lost it and couldn't find it, even tho' I put it in it's home. So I needed a calculator, so went back to Staples and bot TWO more. (Remember, they are CHEAP and high quality). So I was using it for a bit when I found the original hiding under some metal in it's home spot! So now I have a blue one and a white one. NIce.

 

[Steamchick]

I must see what calculators are available, cheap, here. I mostly do stress calcs, so don't need stats. I like buttons and managing my own calculations, even though if I have a lot I write stuff on spreadsheets on the PC. (I hate the tablet!).
On pinning cranks. A hole through the middle of a journal is a big stress raiser, especially for combined bending and torsional stresses. A partial notch on the tangent is less stressful, but the loss of outer diameter must be considered as well as the stress concentration.
K2

 

[terryd]

I must see what calculators are available, cheap, here. I mostly do stress calcs, so don't need stats. I like buttons and managing my own calculations, even though if I have a lot I write stuff on spreadsheets on the PC. (I hate the tablet!).
On pinning cranks. A hole through the middle of a journal is a big stress raiser, especially for combined bending and torsional stresses. A partial notch on the tangent is less stressful, but the loss of outer diameter must be considered as well as the stress concentration.
K2

Hi K2,
It is also possible to use a small longitudinal pin centred on the circumference of the journal/crankpin.

On another topic I lovedusing my slide rule and tookan advanced course in it's use - it's amazing what one can do with them. Unfortunately my old and trusty 11" Aristo-Darmstadt lost its slider somewhere among my many moves.

Regards
TerrD

 

[terryd]

I must see what calculators are available, cheap, here. I mostly do stress calcs, so don't need stats. I like buttons and managing my own calculations, even though if I have a lot I write stuff on spreadsheets on the PC. (I hate the tablet!).
On pinning cranks. A hole through the middle of a journal is a big stress raiser, especially for combined bending and torsional stresses. A partial notch on the tangent is less stressful, but the loss of outer diameter must be considered as well as the stress concentration.
K2

I have a great Casio scientific cLCULtor from the 1980s and still going strong. I've had many over hte years but the Casio is still the best. I must admit though there days I use tablet or PC based calculators of which there are a lot for different purposes. I even have older iPods (4 & 6 - about the size of a pocket calculator) which have a great range of calculators and an accurate clinometer/bubble level.

TerryD

 

[IanN]

Yes, but - all you need to do is add a round function and format the cells accordingly.

In the 80’s I had to explain to a recent engineering graduate that even though the calculator gave an answer to 8 significant figures, based on the data being collected and utilized only the first 2 to 3 places mattered in the final answer. We lost a lot of common sense when we stopped using slide rules.

Hi Chazz,

I agree totally with your comments, but look at it from the point of view of the people creating Solidworks:

If they display the mm/in conversion result to the full resolution of the software, they will be mocked by some people for quoting to a unnecessary number of figures.

If they round the conversion results to a specific degree of accuracy, there will be another group of people who will criticise them for the rounding errors in the conversion.

You are damned if you do and damned if you don't......

But remember that Solidworks is a proper, heavy duty, commercial piece of software intended to be used in industry, not by enthusiastic amateurs for whom engineering is an enjoyable hobby. Surely the most sensible approach is to show excessive accuracy and allow each user to round the results as they require? Of course this does assume that the person using the numbers has the intelligence to do the rounding process and understands 'what is going on' rather than just jeer at the numbers in the table.

I like your comment about slide rules. I have been using machine tools since the late 1960s and left the industry in the mid 1990s to change to a career in education. Since then I have taught engineering both to undergraduates at university and to engineering apprentices. I still use slide rules as a practical tool to demonstrate the concept and application of logarithms - my students create (using CAD) and print their own slide rules (only the C and D scales). Once they can multiply and divide, they very quickly grasp the idea of using the slide rule as a look-up table (for squares, cubes, roots, trig. functions, etc) and I have about 20 slide rules of varying complexity and obscure usage that they then play with.

The slide rule that always impresses students is my Otis King - the clever construction of the scales in a helix around a cylindrical body giving a 60 inch long scale in a device that is the size of a beer can but half the diameter always impresses.

Ian

Yes, but - all you need to do is add a round function and format the cells accordingly.

In the 80’s I had to explain to a recent engineering graduate that even though the calculator gave an answer to 8 significant figures, based on the data being collected and utilized only the first 2 to 3 places mattered in the final answer. We lost a lot of common sense when we stopped using slide rules.

 

[ChazzC]

Hi Chazz,

I agree totally with your comments, but look at it from the point of view of the people creating Solidworks:

If they display the mm/in conversion result to the full resolution of the software, they will be mocked by some people for quoting to a unnecessary number of figures.

If they round the conversion results to a specific degree of accuracy, there will be another group of people who will criticise them for the rounding errors in the conversion.

You are damned if you do and damned if you don't......

But remember that Solidworks is a proper, heavy duty, commercial piece of software intended to be used in industry, not by enthusiastic amateurs for whom engineering is an enjoyable hobby. Surely the most sensible approach is to show excessive accuracy and allow each user to round the results as they require? Of course this does assume that the person using the numbers has the intelligence to do the rounding process and understands 'what is going on' rather than just jeer at the numbers in the table.


Ian

I admit that I'm not familiar with SolidWorks, but all of the CAD packages I have used (all Mac, starting with ClarisCAD, then Ashlar Vellum [a very HD package] and now MacDraft Pro), and have managed (AutoCAD & Revit, both high-end packages) have the capability of selecting precision/number of significant figures. If SolidWorks doesn't have this capability, it's something they should add (otherwise end users of the output are going to go crazy with dimensions like 41/128" instead of 5/16").

 

[Richard Hed]

Hi Chazz,

I agree totally with your comments, but look at it from the point of view of the people creating Solidworks:

If they display the mm/in conversion result to the full resolution of the software, they will be mocked by some people for quoting to a unnecessary number of figures.

If they round the conversion results to a specific degree of accuracy, there will be another group of people who will criticise them for the rounding errors in the conversion.

You are damned if you do and damned if you don't......

But remember that Solidworks is a proper, heavy duty, commercial piece of software intended to be used in industry, not by enthusiastic amateurs for whom engineering is an enjoyable hobby. Surely the most sensible approach is to show excessive accuracy and allow each user to round the results as they require? Of course this does assume that the person using the numbers has the intelligence to do the rounding process and understands 'what is going on' rather than just jeer at the numbers in the table.

I like your comment about slide rules. I have been using machine tools since the late 1960s and left the industry in the mid 1990s to change to a career in education. Since then I have taught engineering both to undergraduates at university and to engineering apprentices. I still use slide rules as a practical tool to demonstrate the concept and application of logarithms - my students create (using CAD) and print their own slide rules (only the C and D scales). Once they can multiply and divide, they very quickly grasp the idea of using the slide rule as a look-up table (for squares, cubes, roots, trig. functions, etc) and I have about 20 slide rules of varying complexity and obscure usage that they then play with.

The slide rule that always impresses students is my Otis King - the clever construction of the scales in a helix around a cylindrical body giving a 60 inch long scale in a device that is the size of a beer can but half the diameter always impresses.

Ian

Can you show us a photo of that Otis King? Thanx

 

[L98fiero]

I got a couple cheapos (but good quality and plenty of functions) for using in my shop. However, I lost it and couldn't find it, even tho' I put it in it's home. So I needed a calculator, so went back to Staples and bot TWO more. (Remember, they are CHEAP and high quality). So I was using it for a bit when I found the original hiding under some metal in it's home spot! So now I have a blue one and a white one. NIce.

See, that's the way it works, buy a new one and you'll find the old one! I think, if it isn't, it should be one of Murphy's Laws.

 

[TimTaylor]

I must see what calculators are available, cheap, here. I mostly do stress calcs, so don't need stats. I like buttons and managing my own calculations, even though if I have a lot I write stuff on spreadsheets on the PC. (I hate the tablet!).
On pinning cranks. A hole through the middle of a journal is a big stress raiser, especially for combined bending and torsional stresses. A partial notch on the tangent is less stressful, but the loss of outer diameter must be considered as well as the stress concentration.
K2

I agree on pinning the crank - creates a potential failure point. Rather than a press/interference fit with loctite, I'd probably go with a shrink fit. Alternatively, depending on the materials, silver brazing or a couple small fusion tacks with a TIG torch would work as well.